Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Thu, 25 Sep 2008 18:40:28 -0500 Milton Miller [EMAIL PROTECTED] wrote: (I trimmed the cc list for the implementation discussion). Yep, good thing. snip Whoops, my bad, in the non threaded case, there's no mask at all, only an unmask+eoi at the end, maybe that's an oversight! No, not an oversight. The point is, don't mask/unmask between ack/eoi while handling the interrupt. For many irq controllers, the eoi must be done from the same cpu, hence the mask and eoi before actually handling the interrupt in the general case. Its a feature of xics that we don't have to play that game, but can do the cpu and device eoi separately. Ok, will try to play with this a bit more. snip That may be, but I'm only looking at the code (read no specifications at hand) and it looks like a black box to me. PowerPC External Interrupt Architecture is defined in appendix A of Power.org Standard for Power Architecture Platform Requirements (Workstation, Server), available to Power.org members. The developer-level membership in Power.org is free. (see www.power.org). I already have that one and started to dig into the interrupt stuff, but as with all normative stuff it's boring to the extreme and not always without flaws. Looks like I know what I'll be reading this WE. That said, it likely won't mention the eHEA in enough detail to note that the interrupt gets cleared on unmask. On the other hand, I have actually seen the source to implementations of the xics logic, so I have a very good understanding of it (and know of a few implementation features, shall we say). Good to know. The path lengh for mask and unmask is always VERY slow and single threaded global lock and single context in xics. It is designed and tuned to run at driver startup and shutdown (and adapter reset and reinitalize during pci error processing), not during normal irq processing. Now, that is quite interesting then. Those mask() and unmask() should then be called shutdown() and startup() and not at each interrupt or am I misunderstanding you. Basically, yes. but linux likes to let drivers mask at other times, and that is the facility we have. Darn, do those drivers really need that heavywheight masking at the source or something simpler could be accomplished by fiddling with the processor priority in mask and unmask? The XICS hardware implicitly masks the specific source as part of interrupt ack (get_irq), and implicitly undoes this mask at eoi. In addition, it helps to manage the cpu priority by supplying the previous priority as part of the get_irq process and providing for the priority to be restored (lowered only) as part of the eoi. The hardware does support setting the cpu priority independently. This confirms, then, that the mask and unmask methods should be empty for the xics. We should only be using this implicit masking for xics, and not the explicit masking for any normal interrupt processing. OK I don't know if this means making the mask/unmask setting a bit in software, Used by whom? The thought here was if we can't change the caller, then maybe we could try to figure out what the caller was trying to accomplish and defer what was requested based on context. Obviously, we are better off changing the caller. That will not be so easy as we'll change behaviour for every user of the genirq layer. and the enable/disable to actually call what we do now on mask/unmask, or if it means we need a new flow type on real time. Maybe a new flow type is not necessary considering what you said. Maybe not, but I think it would be preferred ... we do have the source to both sides. That's straightforward to do in the non threaded case, however, in the threaded case the xics code would have to also manage the hardirq thread as we would not be able to reuse the generic one (because of the unmask it does at the very end). snip I think the flows we want on xics are: (non-threaded) getirq (implicit source specific mask until eoi) handle interrupt eoi (implicit cpu priority restore) Yep (threaded) getirq (implicit source specific mask until eoi) explicit cpu priority restore ^ How do you go about doing that? Still not clear to me. xics_set_cpu_priority(0xff) OK of course, there needs to be some kind of struct irq_chip method to call it. Yep, excepted that it's currently not provided by irq_chip. handle interrupt eoi (implicit cpu priority restore to same as explicit level) Where the cpu priority restore allows receiving other interrupts of the same priority from the hardware. So I guess the question is can the rt kernel interrupt processing take advantage of xics auto mask,
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Thu, 25 Sep 2008 07:15:17 +1000 Benjamin Herrenschmidt [EMAIL PROTECTED] wrote: On Wed, 2008-09-24 at 14:35 +0200, Sebastien Dugue wrote: Hi Ben, On Wed, 24 Sep 2008 20:17:47 +1000 Benjamin Herrenschmidt [EMAIL PROTECTED] wrote: On Wed, 2008-09-24 at 04:58 -0500, Milton Miller wrote: The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded global context, which in addition to increasing path length will really limit scalability. The interrupt controller poll and reject facilities are accessed through hypervisor calls which are comparable to a fast syscall, and parallel to all cpus. Note also that the XICS code thus assumes, iirc, as does the cell IIC code, that eoi is called on the -same- cpu that fetched the interrupt initially. That assumption can be broken with IRQ threads no ? No, the fetch and the eoi are both done in interrupt context before the hardirq thread is woken up. On the other hand, the mask+eoi and the unmask may well happen on different cpus as there's only one hardirq thread per irq on the system. Don't know if this is a problem with the XICS though. Ok, that's the right approach then. It should work. I don't know what the specific problems with HEA are at this stage. Yep, except as it behaves in way that the current -rt fasteoi flow cannot handle. It doesn't seem to make sense to implement a set_irq_type(), what would it do ? The XICS doesn't expose any concept of interrupt type... That's what I gathered from looking at the sources. Thanks, Sebastien. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Thu, 2008-09-25 at 09:18 +0200, Sebastien Dugue wrote: Ok, that's the right approach then. It should work. I don't know what the specific problems with HEA are at this stage. Yep, except as it behaves in way that the current -rt fasteoi flow cannot handle. We probably need to make a special xics flow handler for -rt that does what Milton suggested, ie, bring down the CPU priority right away and only EOI later or something like that, instead of masking/unmasking. I don't know what are the other potential issues with the HEA though. Ben. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Thu, 25 Sep 2008 07:14:07 +1000 Benjamin Herrenschmidt [EMAIL PROTECTED] wrote: There may be some implicit assumption in that we expect the cpu priority to be returned to normal by the EOI, but there is nothing in the hardware that requires the EOI to come from the same cpu as accepted the interrupt for processing, with the exception of the IPI which is per-cpu (and the only interrupt that is per-cpu). Well, there is one fundamental one: The XIRR register we access is per-CPU, so if we are to return the right processor priority, we must make sure we write the right XIRR. That's already the case as the irq fetch (xx_xirr_info_get()) and eoi (xx_xirr_info_set()) are both done in interrupt context, therefore on the same cpu. Same with Cell, MPIC, actually and a few others. In general I'd say most fast_eoi type PICs have this requirement. It would probably mean adding the concept of the current cpu priority vs interrupts and making sure we write it to hardware at irq_exit() time when deferring the actual irq handlers. I think we need something like a special -rt variant of the fast_eoi handler that masks eoi's in ack() before the thread is spun off, and unmasks instead of eoi() when the irq processing is complete. This is what is already done in the threaded case: - fetch + mask + eoi in interrupt context - unmask in the thread when processing is complete. Sebastien. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Thu, 25 Sep 2008 17:22:41 +1000 Benjamin Herrenschmidt [EMAIL PROTECTED] wrote: On Thu, 2008-09-25 at 09:18 +0200, Sebastien Dugue wrote: Ok, that's the right approach then. It should work. I don't know what the specific problems with HEA are at this stage. Yep, except as it behaves in way that the current -rt fasteoi flow cannot handle. We probably need to make a special xics flow handler for -rt that does what Milton suggested, ie, bring down the CPU priority right away Do you mean creating a custom fasteoi handler into xics.c? Also, it's not clear to me from looking at the code how you go about changing the cpu priority. and only EOI later or something like that, instead of masking/unmasking. I don't know what are the other potential issues with the HEA though. Don't know either, but that I can test. Thanks, Sebastien. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Do you mean creating a custom fasteoi handler into xics.c? Also, it's not clear to me from looking at the code how you go about changing the cpu priority. Yup. I think the priority is the CPPR.. Milton can give you more details, if not, I'll pick it up tomorrow when at the office. Ben. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Thu, 25 Sep 2008 18:36:19 +1000 Benjamin Herrenschmidt [EMAIL PROTECTED] wrote: Do you mean creating a custom fasteoi handler into xics.c? Also, it's not clear to me from looking at the code how you go about changing the cpu priority. Yup. I think the priority is the CPPR.. Milton can give you more details, if not, I'll pick it up tomorrow when at the office. Thanks Ben, will look into this. Nite Sebastien. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Wed, 24 Sep 2008 11:42:15 -0500 Milton Miller [EMAIL PROTECTED] wrote: On Sep 24, 2008, at 7:30 AM, Sebastien Dugue wrote: Hi Milton, On Wed, 24 Sep 2008 04:58:22 -0500 (CDT) Milton Miller [EMAIL PROTECTED] wrote: On Mon Sep 15 at 18:04:06 EST in 2008, Sebastien Dugue wrote: When entering the low level handler, level sensitive interrupts are masked, then eio'd in interrupt context and then unmasked at the end of hardirq processing. That's fine as any interrupt comming in-between will still be processed since the kernel replays those pending interrupts. Is this to generate some kind of software managed nesting and priority of the hardware level interrupts? No, not really. This is only to be sure to not miss interrupts coming from the same source that were received during threaded hardirq processing. Some instrumentation showed that it never seems to happen in the eHEA interrupt case, so I think we can forget this aspect. I don't trust the interrupt can never happen during hea hardirq, because I think there will be a race between their rearming the next interrupt and the unmask being called. So do I, it was just to make sure I was not hit by another interrupt while handling the previous one and thus reduce the number of hypothesis. I sure do not say that it cannot happen, just that that path is not taken when I have the eHEA hang. I was trying to understand why the mask and early eoi, but I guess its to handle other more limited interrupt controllers where the interrupts stack in hardware instead of software. Also, the problem only manifests with the eHEA RX interrupt. For example, the IBM Power Raid (ipr) SCSI exhibits absolutely no problem under an RT kernel. From this I conclude that: IPR - PCI - XICS is OK eHEA - IBMEBUS - XICS is broken with hardirq preemption. I also checked that forcing the eHEA interrupt to take the non threaded path does work. For a long period of time, XICS dealt only with level interrupts. First Micro Channel, and later PCI buses. The IPI is made level by software conventions. Recently, EHCA, EHEA, and MSI interrupts were added which by their nature are edge based. The logic that converts those interrupts to the XICS layer is responsible for the resend when no cpu can accept them, but not to retrigger after an EOI. OK Here is a side by side comparison of the fasteoi flow with and without hardirq threading (sorry it's a bit wide) (removed) the non-threaded flow does (in interrupt context): mask Whoops, my bad, in the non threaded case, there's no mask at all, only an unmask+eoi at the end, maybe that's an oversight! handle interrupt unmask eoi the threaded flow does: mask eoi handle interrupt unmask If I remove the mask() call, then the eHEA is no longer hanging. Hmm, I guess I'm confused. You are saying the irq does not appear if it occurs while it is masked? Looks like it is, but I cannot say for sure, the only observable effect is that I do not get any more interrupts coming from the eHEA. Well, in that case, I would guess that the hypervisor is checking if the irq is previously pending while it was masked and resetting it as part of the unmask. It can't do it on level, but can on the true edge sources. I would further say the justification for this might be the hardware might make it pending from some previous stale event that might result in the false interrupt on startup were it not to do this clear. The reason I ask is the xics controller can do unlimited nesting of hardware interrupts. In fact, the hardware has 255 levels of priority, of which 16 or so are reserved by the hypervisor, leaving over 200 for the os to manage. Higher numbers are lower in priority, and the hardware will only dispatch an interrupt to a given cpu if it is currenty at a lower priority. If it is at a higher priority and the interrupt is not bound to a specific cpu it will look for another cpu to dispatch it. The hardware will not re-present an irq until the it is EOId (managed by a small state machine per interrupt at the source, which also handles no cpu available try again later), but software can return its cpu priority to the previous level to recieve other interrupt sources at the same level. The hardware also supports lazy update of the cpu priority register when an interrupt is presented; as long as the cpu is hard-irq enabled it can take the irq then write is real priority and let the hw decide if the irq is still pending or it must defer or try another cpu in the rejection scenerio. The only restriction is that the EOI can not cause an interrupt reject by raising the priority while sending the EOI command. The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
(I trimmed the cc list for the implementation discussion). On Wed, 24 Sep 2008 11:42:15 -0500 Milton Miller [EMAIL PROTECTED] wrote: On Sep 24, 2008, at 7:30 AM, Sebastien Dugue wrote: Hi Milton, On Wed, 24 Sep 2008 04:58:22 -0500 (CDT) Milton Miller [EMAIL PROTECTED] wrote: On Mon Sep 15 at 18:04:06 EST in 2008, Sebastien Dugue wrote: When entering the low level handler, level sensitive interrupts are masked, then eio'd in interrupt context and then unmasked at the end of hardirq processing. That's fine as any interrupt comming in-between will still be processed since the kernel replays those pending interrupts. Is this to generate some kind of software managed nesting and priority of the hardware level interrupts? No, not really. This is only to be sure to not miss interrupts coming from the same source that were received during threaded hardirq processing. Some instrumentation showed that it never seems to happen in the eHEA interrupt case, so I think we can forget this aspect. I don't trust the interrupt can never happen during hea hardirq, because I think there will be a race between their rearming the next interrupt and the unmask being called. So do I, it was just to make sure I was not hit by another interrupt while handling the previous one and thus reduce the number of hypothesis. I sure do not say that it cannot happen, just that that path is not taken when I have the eHEA hang. I was trying to understand why the mask and early eoi, but I guess its to handle other more limited interrupt controllers where the interrupts stack in hardware instead of software. Also, the problem only manifests with the eHEA RX interrupt. For example, the IBM Power Raid (ipr) SCSI exhibits absolutely no problem under an RT kernel. From this I conclude that: IPR - PCI - XICS is OK eHEA - IBMEBUS - XICS is broken with hardirq preemption. I also checked that forcing the eHEA interrupt to take the non threaded path does work. For a long period of time, XICS dealt only with level interrupts.First Micro Channel, and later PCI buses. The IPI is made level by software conventions. Recently, EHCA, EHEA, and MSI interrupts were added which by their nature are edge based. The logic that converts those interrupts to the XICS layer is responsible for the resend when no cpu can accept them, but not to retrigger after an EOI. OK Here is a side by side comparison of the fasteoi flow with and without hardirq threading (sorry it's a bit wide) (removed) the non-threaded flow does (in interrupt context): mask Whoops, my bad, in the non threaded case, there's no mask at all, only an unmask+eoi at the end, maybe that's an oversight! No, not an oversight. The point is, don't mask/unmask between ack/eoi while handling the interrupt. For many irq controllers, the eoi must be done from the same cpu, hence the mask and eoi before actually handling the interrupt in the general case. Its a feature of xics that we don't have to play that game, but can do the cpu and device eoi separately. handle interrupt unmask eoi the threaded flow does: mask eoi handle interrupt unmask If I remove the mask() call, then the eHEA is no longer hanging. Hmm, I guess I'm confused. You are saying the irq does not appear if it occurs while it is masked? Looks like it is, but I cannot say for sure, the only observable effect is that I do not get any more interrupts coming from the eHEA. (removed features of xics) That may be, but I'm only looking at the code (read no specifications at hand) and it looks like a black box to me. PowerPC External Interrupt Architecture is defined in appendix A of Power.org Standard for Power Architecture Platform Requirements (Workstation, Server), available to Power.org members. The developer-level membership in Power.org is free. (see www.power.org). That said, it likely won't mention the eHEA in enough detail to note that the interrupt gets cleared on unmask. On the other hand, I have actually seen the source to implementations of the xics logic, so I have a very good understanding of it (and know of a few implementation features, shall we say). The path lengh for mask and unmask is always VERY slow and single threaded global lock and single context in xics. It is designed and tuned to run at driver startup and shutdown (and adapter reset and reinitalize during pci error processing), not during normal irq processing. Now, that is quite interesting then. Those mask() and unmask() should then be called shutdown() and startup() and not at each interrupt or am I misunderstanding you. Basically, yes. but linux likes to let drivers mask at other times, and that
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Jan-Bernd wrote: Ben, can you / your team look into the implementation of the set_irq_type functionality needed for XICS? I'm not volunteering to look at or implement any changes for how xics works with generic irq, but I'm trying to understand what the rt kernel is trying to accomplish with this statement: On Mon Sep 15 at 18:04:06 EST in 2008, Sebastien Dugue wrote: When entering the low level handler, level sensitive interrupts are masked, then eio'd in interrupt context and then unmasked at the end of hardirq processing. That's fine as any interrupt comming in-between will still be processed since the kernel replays those pending interrupts. Is this to generate some kind of software managed nesting and priority of the hardware level interrupts? The reason I ask is the xics controller can do unlimited nesting of hardware interrupts. In fact, the hardware has 255 levels of priority, of which 16 or so are reserved by the hypervisor, leaving over 200 for the os to manage. Higher numbers are lower in priority, and the hardware will only dispatch an interrupt to a given cpu if it is currenty at a lower priority. If it is at a higher priority and the interrupt is not bound to a specific cpu it will look for another cpu to dispatch it. The hardware will not re-present an irq until the it is EOId (managed by a small state machine per interrupt at the source, which also handles no cpu available try again later), but software can return its cpu priority to the previous level to recieve other interrupt sources at the same level. The hardware also supports lazy update of the cpu priority register when an interrupt is presented; as long as the cpu is hard-irq enabled it can take the irq then write is real priority and let the hw decide if the irq is still pending or it must defer or try another cpu in the rejection scenerio. The only restriction is that the EOI can not cause an interrupt reject by raising the priority while sending the EOI command. The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded global context, which in addition to increasing path length will really limit scalability. The interrupt controller poll and reject facilities are accessed through hypervisor calls which are comparable to a fast syscall, and parallel to all cpus. We used to lower the priority to allow other interrupts in, but we realized that in addition to the questionable latency in doing so, it only caused unlimited stack nesting and overflow without per-irq stacks. We currently set IPIs above other irqs so we typically only process them during a hard irq (but we return to base level after IPI and could take another base irq, a bug). So, Sebastien, with this information, is does the RT kernel have a strategy that better matches this hardware? milton ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Wed, 2008-09-24 at 04:58 -0500, Milton Miller wrote: The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded global context, which in addition to increasing path length will really limit scalability. The interrupt controller poll and reject facilities are accessed through hypervisor calls which are comparable to a fast syscall, and parallel to all cpus. Note also that the XICS code thus assumes, iirc, as does the cell IIC code, that eoi is called on the -same- cpu that fetched the interrupt initially. That assumption can be broken with IRQ threads no ? Ben. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Sep 24, 2008, at 5:17 AM, Benjamin Herrenschmidt wrote: On Wed, 2008-09-24 at 04:58 -0500, Milton Miller wrote: The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded global context, which in addition to increasing path length will really limit scalability. The interrupt controller poll and reject facilities are accessed through hypervisor calls which are comparable to a fast syscall, and parallel to all cpus. Note also that the XICS code thus assumes, iirc, as does the cell IIC code, that eoi is called on the -same- cpu that fetched the interrupt initially. That assumption can be broken with IRQ threads no ? There may be some implicit assumption in that we expect the cpu priority to be returned to normal by the EOI, but there is nothing in the hardware that requires the EOI to come from the same cpu as accepted the interrupt for processing, with the exception of the IPI which is per-cpu (and the only interrupt that is per-cpu). It would probably mean adding the concept of the current cpu priority vs interrupts and making sure we write it to hardware at irq_exit() time when deferring the actual irq handlers. The MPIC hardware, on the other hand, maintains a queue of pending interrupts (It has been about a decade but the number 4-5 comes to mind), and the hardware must receive the EOI on the cpu that took it. I am guessing that the handling described (take level irq, mask it, eoi it, dispatch the thread, then unmask it after processing) is a result to work within those limitations. Do you know the cell IIC to know if its mpic or xics in this regard? The other unknown is the (very few) platforms that present as xics but are really firmware on mpic. If they do a full virtual layer and don't take shortcuts but do eoi/mask like described here they should work, but I would not be surprised that does not hold true :-(. milton ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Hi Milton, On Wed, 24 Sep 2008 04:58:22 -0500 (CDT) Milton Miller [EMAIL PROTECTED] wrote: Jan-Bernd wrote: Ben, can you / your team look into the implementation of the set_irq_type functionality needed for XICS? I'm not volunteering to look at or implement any changes for how xics works with generic irq, but I'm trying to understand what the rt kernel is trying to accomplish with this statement: On Mon Sep 15 at 18:04:06 EST in 2008, Sebastien Dugue wrote: When entering the low level handler, level sensitive interrupts are masked, then eio'd in interrupt context and then unmasked at the end of hardirq processing. That's fine as any interrupt comming in-between will still be processed since the kernel replays those pending interrupts. Is this to generate some kind of software managed nesting and priority of the hardware level interrupts? No, not really. This is only to be sure to not miss interrupts coming from the same source that were received during threaded hardirq processing. Some instrumentation showed that it never seems to happen in the eHEA interrupt case, so I think we can forget this aspect. Also, the problem only manifests with the eHEA RX interrupt. For example, the IBM Power Raid (ipr) SCSI exhibits absolutely no problem under an RT kernel. From this I conclude that: IPR - PCI - XICS is OK eHEA - IBMEBUS - XICS is broken with hardirq preemption. I also checked that forcing the eHEA interrupt to take the non threaded path does work. Here is a side by side comparison of the fasteoi flow with and without hardirq threading (sorry it's a bit wide) fasteoi flow: Non threaded hardirq| threaded hardirq | interrupt context| interrupt context hardirq thread -| - -- | | clear IRQ_REPLAY and IRQ_WAITING| clear IRQ_REPLAY and IRQ_WAITING | increment percpu interrupt count| increment percpu interrupt count | if no action or IRQ_INPROGRESS or IRQ_DISABLED | if no action or IRQ_INPROGRESS or IRQ_DISABLED | set IRQ_PENDING | set IRQ_PENDING | mask | mask | eoi | eoi | done | done | set IRQ_INPROGRESS | set IRQ_INPROGRESS | | | wakeup IRQ thread | | mask | | eoi | | done -- | \ | \ | \ | -- loop | clear IRQ_PENDING | clear IRQ_PENDING | call handle_IRQ_event | call handle_IRQ_event | | check for prempt | | until IRQ_PENDING cleared | | clear IRQ_INPROGRESS| clear IRQ_INPROGRESS | if not IRQ_DISABLED |
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Hi Ben, On Wed, 24 Sep 2008 20:17:47 +1000 Benjamin Herrenschmidt [EMAIL PROTECTED] wrote: On Wed, 2008-09-24 at 04:58 -0500, Milton Miller wrote: The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded global context, which in addition to increasing path length will really limit scalability. The interrupt controller poll and reject facilities are accessed through hypervisor calls which are comparable to a fast syscall, and parallel to all cpus. Note also that the XICS code thus assumes, iirc, as does the cell IIC code, that eoi is called on the -same- cpu that fetched the interrupt initially. That assumption can be broken with IRQ threads no ? No, the fetch and the eoi are both done in interrupt context before the hardirq thread is woken up. On the other hand, the mask+eoi and the unmask may well happen on different cpus as there's only one hardirq thread per irq on the system. Don't know if this is a problem with the XICS though. Thanks, Sebastien. Ben. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Sep 24, 2008, at 7:30 AM, Sebastien Dugue wrote: Hi Milton, On Wed, 24 Sep 2008 04:58:22 -0500 (CDT) Milton Miller [EMAIL PROTECTED] wrote: On Mon Sep 15 at 18:04:06 EST in 2008, Sebastien Dugue wrote: When entering the low level handler, level sensitive interrupts are masked, then eio'd in interrupt context and then unmasked at the end of hardirq processing. That's fine as any interrupt comming in-between will still be processed since the kernel replays those pending interrupts. Is this to generate some kind of software managed nesting and priority of the hardware level interrupts? No, not really. This is only to be sure to not miss interrupts coming from the same source that were received during threaded hardirq processing. Some instrumentation showed that it never seems to happen in the eHEA interrupt case, so I think we can forget this aspect. I don't trust the interrupt can never happen during hea hardirq, because I think there will be a race between their rearming the next interrupt and the unmask being called. I was trying to understand why the mask and early eoi, but I guess its to handle other more limited interrupt controllers where the interrupts stack in hardware instead of software. Also, the problem only manifests with the eHEA RX interrupt. For example, the IBM Power Raid (ipr) SCSI exhibits absolutely no problem under an RT kernel. From this I conclude that: IPR - PCI - XICS is OK eHEA - IBMEBUS - XICS is broken with hardirq preemption. I also checked that forcing the eHEA interrupt to take the non threaded path does work. For a long period of time, XICS dealt only with level interrupts. First Micro Channel, and later PCI buses. The IPI is made level by software conventions. Recently, EHCA, EHEA, and MSI interrupts were added which by their nature are edge based. The logic that converts those interrupts to the XICS layer is responsible for the resend when no cpu can accept them, but not to retrigger after an EOI. Here is a side by side comparison of the fasteoi flow with and without hardirq threading (sorry it's a bit wide) (removed) the non-threaded flow does (in interrupt context): mask handle interrupt unmask eoi the threaded flow does: mask eoi handle interrupt unmask If I remove the mask() call, then the eHEA is no longer hanging. Hmm, I guess I'm confused. You are saying the irq does not appear if it occurs while it is masked? Well, in that case, I would guess that the hypervisor is checking if the irq is previously pending while it was masked and resetting it as part of the unmask. It can't do it on level, but can on the true edge sources. I would further say the justification for this might be the hardware might make it pending from some previous stale event that might result in the false interrupt on startup were it not to do this clear. The reason I ask is the xics controller can do unlimited nesting of hardware interrupts. In fact, the hardware has 255 levels of priority, of which 16 or so are reserved by the hypervisor, leaving over 200 for the os to manage. Higher numbers are lower in priority, and the hardware will only dispatch an interrupt to a given cpu if it is currenty at a lower priority. If it is at a higher priority and the interrupt is not bound to a specific cpu it will look for another cpu to dispatch it. The hardware will not re-present an irq until the it is EOId (managed by a small state machine per interrupt at the source, which also handles no cpu available try again later), but software can return its cpu priority to the previous level to recieve other interrupt sources at the same level. The hardware also supports lazy update of the cpu priority register when an interrupt is presented; as long as the cpu is hard-irq enabled it can take the irq then write is real priority and let the hw decide if the irq is still pending or it must defer or try another cpu in the rejection scenerio. The only restriction is that the EOI can not cause an interrupt reject by raising the priority while sending the EOI command. The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded global context, which in addition to increasing path length will really limit scalability. The interrupt controller poll and reject facilities are accessed through hypervisor calls which are comparable to a fast syscall, and parallel to all cpus. We used to lower the priority to allow other interrupts in, but we realized that in addition to the questionable latency in doing so, it only caused unlimited stack nesting and overflow without per-irq stacks. We currently set IPIs above other irqs so we typically only process them during a hard irq (but we return to base level after IPI and could take another base irq, a bug). So, Sebastien, with this information, is does the RT kernel have a strategy that better matches this
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
There may be some implicit assumption in that we expect the cpu priority to be returned to normal by the EOI, but there is nothing in the hardware that requires the EOI to come from the same cpu as accepted the interrupt for processing, with the exception of the IPI which is per-cpu (and the only interrupt that is per-cpu). Well, there is one fundamental one: The XIRR register we access is per-CPU, so if we are to return the right processor priority, we must make sure we write the right XIRR. Same with Cell, MPIC, actually and a few others. In general I'd say most fast_eoi type PICs have this requirement. It would probably mean adding the concept of the current cpu priority vs interrupts and making sure we write it to hardware at irq_exit() time when deferring the actual irq handlers. I think we need something like a special -rt variant of the fast_eoi handler that masks eoi's in ack() before the thread is spun off, and unmasks instead of eoi() when the irq processing is complete. Ben. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Wed, 2008-09-24 at 14:35 +0200, Sebastien Dugue wrote: Hi Ben, On Wed, 24 Sep 2008 20:17:47 +1000 Benjamin Herrenschmidt [EMAIL PROTECTED] wrote: On Wed, 2008-09-24 at 04:58 -0500, Milton Miller wrote: The per-interrupt mask and unmask calls have to go through RTAS, a single-threaded global context, which in addition to increasing path length will really limit scalability. The interrupt controller poll and reject facilities are accessed through hypervisor calls which are comparable to a fast syscall, and parallel to all cpus. Note also that the XICS code thus assumes, iirc, as does the cell IIC code, that eoi is called on the -same- cpu that fetched the interrupt initially. That assumption can be broken with IRQ threads no ? No, the fetch and the eoi are both done in interrupt context before the hardirq thread is woken up. On the other hand, the mask+eoi and the unmask may well happen on different cpus as there's only one hardirq thread per irq on the system. Don't know if this is a problem with the XICS though. Ok, that's the right approach then. It should work. I don't know what the specific problems with HEA are at this stage. It doesn't seem to make sense to implement a set_irq_type(), what would it do ? The XICS doesn't expose any concept of interrupt type... Ben. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Wed, 2008-09-24 at 11:42 -0500, Milton Miller wrote: I was trying to understand why the mask and early eoi, but I guess its to handle other more limited interrupt controllers where the interrupts stack in hardware instead of software. No Milton, we must do it that way, because the EOI must be done on the right CPU even on XICS, or we won't get the CPU priority back properly. Ben. ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Sep 24, 2008, at 4:16 PM, Benjamin Herrenschmidt wrote: On Wed, 2008-09-24 at 11:42 -0500, Milton Miller wrote: I was trying to understand why the mask and early eoi, but I guess its to handle other more limited interrupt controllers where the interrupts stack in hardware instead of software. No Milton, we must do it that way, because the EOI must be done on the right CPU even on XICS, or we won't get the CPU priority back properly. Ben and I had a online chat, and he pointed out I needed to be more specific in saying what I was thinking. I think the flows we want on xics are: (non-threaded) getirq (implicit source specific mask until eoi) handle interrupt eoi (implicit cpu priority restore) (threaded) getirq (implicit source specific mask until eoi) explicit cpu priority restore handle interrupt eoi (implicit cpu priority restore to same as explicit level) cpu takes interrupt, checks soft disabled if so, set hard disabled else call get_irq if threaded write cppr to restore this cpu irq dispatch state to non-interrupt mark irq thread as irq pending else handle interrupt eoi (cppr = base) irq thread will handle interrupt eoi wait for marked pending again The part Ben did not follow was that the cppr write to base priority is done by the interrupted cpu (like the mask and eoi in the current flow) and only the final eoi (where the mask is in the existing flow) is done on which ever cpu happens to run the irq thread. (optional) As I was discussing with Paul, when taking an irq when soft-disabled but still hard enabled, it is possible to write the cppr such that it would reject the pending irq and have it be considered for dispatch to another cpu. But it would increase pathlength on both the go-to-hard-disabled and return-from-hard-disabled and the hardware will have some latency as it will likely send it back to the io source until it retrys, so we would only want to do this if the hard-disable period is sufficiently long. milton ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption, eHCA is close
Hi,
I think these are the functional changes that need to be included in
the ibmebus driver. We'll add a RT flag in the final version to enable
these changes only for RT-Linux for now.
Ben, can you / your team look into the implementation
of the set_irq_type functionality needed for XICS?
Regards,
Jan-Bernd Christoph
diff -Nurp b/arch/powerpc/kernel/ibmebus.c a/arch/powerpc/kernel/ibmebus.c
--- b/arch/powerpc/kernel/ibmebus.c 2008-09-22 00:29:55.0 +0200
+++ a/arch/powerpc/kernel/ibmebus.c 2008-09-23 12:04:53.0 +0200
@@ -216,12 +216,16 @@ int ibmebus_request_irq(u32 ist, irq_han
unsigned long irq_flags, const char *devname,
void *dev_id)
{
+ int ret;
unsigned int irq = irq_create_mapping(NULL, ist);
if (irq == NO_IRQ)
return -EINVAL;
- return request_irq(irq, handler, irq_flags, devname, dev_id);
+ ret = request_irq(irq, handler, irq_flags, devname, dev_id);
+ set_irq_type(irq, IRQ_TYPE_EDGE_RISING);
+
+ return ret;
}
EXPORT_SYMBOL(ibmebus_request_irq);
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Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Thu, 18 Sep 2008 09:53:54 +0200 Christoph Raisch [EMAIL PROTECTED] wrote:
Sebastien Dugue [EMAIL PROTECTED] wrote on 15.09.2008 10:04:06:
[PATCH HACK] powerpc: quick hack to get a functional eHEA with
hardirq preemption
Sebastien Dugue
to:
15.09.2008 10:07
Cc:
linux-ppc, linux-kernel, Linux-rt, netdev, Jan-Bernd Themann, Thomas
Q Klein, Christoph Raisch, jean-pierre.dion, gilles.carry, tinytim
WARNING: HACK - HACK - HACK
Not-Signed-off-by: Sebastien Dugue [EMAIL PROTECTED]
---
--- a/arch/powerpc/kernel/ibmebus.c
+++ b/arch/powerpc/kernel/ibmebus.c
@@ -41,6 +41,7 @@
- return request_irq(irq, handler, irq_flags, devname, dev_id);
+ ret = request_irq(irq, handler, irq_flags, devname, dev_id);
+
+ desc = irq_desc + irq;
+ desc-status = ~(IRQ_TYPE_SENSE_MASK | IRQ_LEVEL);
+ desc-status |= IRQ_TYPE_EDGE_RISING;
+
+ return ret;
This looks a bit like a set_irq_type call.
Yep.
Don't know if this is fully implemented for xics though...
No, the xics does not implement a set_type() method.
}
EXPORT_SYMBOL(ibmebus_request_irq);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index b7b397a..6d366ca 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -430,7 +430,7 @@ handle_fasteoi_irq(unsigned int irq, struct
irq_desc *desc)
action = desc-action;
if (unlikely(!action || (desc-status (IRQ_INPROGRESS |
IRQ_DISABLED {
- desc-status |= IRQ_PENDING;
+ desc-status |= IRQ_PENDING | IRQ_MASKED;
if (desc-chip-mask)
desc-chip-mask(irq);
goto out;
@@ -439,9 +439,10 @@ handle_fasteoi_irq(unsigned int irq, struct
irq_desc *desc)
desc-status |= IRQ_INPROGRESS;
/*
* In the threaded case we fall back to a mask+eoi sequence:
+* excepted for edge interrupts which are not masked.
*/
if (redirect_hardirq(desc)) {
- if (desc-chip-mask)
+ if (desc-chip-mask !(desc-status IRQ_TYPE_EDGE_BOTH))
desc-chip-mask(irq);
goto out;
}
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 3bffa20..3e39c71 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -788,9 +788,12 @@ static void do_hardirq(struct irq_desc *desc)
thread_simple_irq(desc);
else if (desc-handle_irq == handle_level_irq)
thread_level_irq(desc);
- else if (desc-handle_irq == handle_fasteoi_irq)
- thread_fasteoi_irq(desc);
- else if (desc-handle_irq == handle_edge_irq)
+ else if (desc-handle_irq == handle_fasteoi_irq) {
+ if (desc-status IRQ_TYPE_EDGE_BOTH)
+ thread_edge_irq(desc);
+ else
+ thread_fasteoi_irq(desc);
+ } else if (desc-handle_irq == handle_edge_irq)
thread_edge_irq(desc);
else
thread_do_irq(desc);
--
1.6.0.1.308.gede4c
According to the specs at some point in the system the HEA IRQs have a edge
characteristic.
But since PCI-E edge and level can both be forwarded through a message
interface
(HEA is not PCI-E, it's only connected to the same internal bus, where the
PHB resides)
Good to know, the problem here seems to be that the xics is using the
fasteoi flow handler, which under unconditionally masks the irq. Will have to
dig in the genirq stuff a bit more to understand what the differences are
between -rt and mainline.
Anybody from the xics experts want to comment on this?
It would be really interresting to know if the eHCA exhibits the same
problem under -rt as it's the only other user of the ibmebus.
Unfortunately I don't have the hardware to test.
Thanks,
Sebastien.
Gruss / Regards
Christoph R. Jan-Bernd
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Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption, eHCA is close
Sebastien Dugue [EMAIL PROTECTED] wrote on 18.09.2008 11:27:13: It would be really interresting to know if the eHCA exhibits the same problem under -rt as it's the only other user of the ibmebus. Unfortunately I don't have the hardware to test. eHCA is very close from the interrupt generation and handling perspective, so yes, could be an issue there as well. Gruss / Regards Christoph Raisch ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption, eHCA is close
On Thu, 18 Sep 2008 12:42:05 +0200 Christoph Raisch [EMAIL PROTECTED] wrote: Sebastien Dugue [EMAIL PROTECTED] wrote on 18.09.2008 11:27:13: It would be really interresting to know if the eHCA exhibits the same problem under -rt as it's the only other user of the ibmebus. Unfortunately I don't have the hardware to test. eHCA is very close from the interrupt generation and handling perspective, so yes, could be an issue there as well. That's what I was speculating. Thanks, Sebastien. Gruss / Regards Christoph Raisch ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
On Mon, Sep 15, 2008 at 03:13:32PM +0200, Sebastien Dugue wrote: [...] we are a bit worried about putting this into the mainstream part of non real time linux. Heck, I sure do not want this to be applied mainstream nor into any tree. The sole purpose of this patch was to trigger some reaction from the people who know the hardware and try to understand where the problem lies. There interrupts work perfectly fine, and it was a bit of a challenge to get there for all cases / configurations / machines. Agreed, but the fact that it fails with hardirq preemption leads me to believe (without any more knowledge about the harware) that there might be something amiss with this driver (or the code concerning the XICS) nevertheless. Could you try to enable these changes only for RT-Linux via a real-time kconfig switch? Nope, this is just a quick hack that allows me to have a functional eHEA under the rt kernel. I want to understand what the problem is: - Is the eHEA really delivering level interrupts to the XICS? - Is the XICS loosing interrupts when they are masked? There is a known bug in the -rt kernels, the bug causes handlers to lose edge interrupts. See this patch: http://lkml.org/lkml/2008/6/30/372 - ...? -- Anton Vorontsov email: [EMAIL PROTECTED] irc://irc.freenode.net/bd2 ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Hi Anton, On Tue, 16 Sep 2008 15:59:47 +0400 Anton Vorontsov [EMAIL PROTECTED] wrote: On Mon, Sep 15, 2008 at 03:13:32PM +0200, Sebastien Dugue wrote: [...] we are a bit worried about putting this into the mainstream part of non real time linux. Heck, I sure do not want this to be applied mainstream nor into any tree. The sole purpose of this patch was to trigger some reaction from the people who know the hardware and try to understand where the problem lies. There interrupts work perfectly fine, and it was a bit of a challenge to get there for all cases / configurations / machines. Agreed, but the fact that it fails with hardirq preemption leads me to believe (without any more knowledge about the harware) that there might be something amiss with this driver (or the code concerning the XICS) nevertheless. Could you try to enable these changes only for RT-Linux via a real-time kconfig switch? Nope, this is just a quick hack that allows me to have a functional eHEA under the rt kernel. I want to understand what the problem is: - Is the eHEA really delivering level interrupts to the XICS? - Is the XICS loosing interrupts when they are masked? There is a known bug in the -rt kernels, the bug causes handlers to lose edge interrupts. See this patch: http://lkml.org/lkml/2008/6/30/372 Yes, I've been following that thread back then and my hack is based on your patch. So yes, it seems to be the same problem and it lies in the way -rt handles the fasteoi flow. But looking at the comments from the XICS code, it seems that its wired for level only interrupts. Therefore without any more specs, it's still not clear to me that there's not a bug with the way the xics handles eHEA interrupts. Are the eHEA interrupts really level interrupts? If so why do they get lost when masked? I just found that not masking that particular interrupt in the fasteoi path makes the thing work! Thanks, Sebastien. - ...? -- Anton Vorontsov email: [EMAIL PROTECTED] irc://irc.freenode.net/bd2 -- To unsubscribe from this list: send the line unsubscribe linux-rt-users in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Hi,
we are a bit worried about putting this into the mainstream part of non
real time linux.
There interrupts work perfectly fine, and it was a bit of a challenge to
get there for all
cases / configurations / machines.
Could you try to enable these changes only for RT-Linux via a real-time
kconfig switch?
This way we make sure we don't break the scheme for eHEA / eHCA.
Regards,
Jan-Bernd Christoph
Sebastien Dugue [EMAIL PROTECTED] wrote on 15.09.2008 10:04:06:
WARNING: HACK - HACK - HACK
Under the RT kernel (with hardirq preemption) the eHEA driver hangs
right
after booting. Fiddling with the hardirqs and softirqs priorities allows
to
run a bit longer but as soon as the network gets under load, the hang
returns. After investigating, it appears that the driver is loosing
interrupts.
To make a long story short, looking at the code, it appears that the
XICS
maps all its interrupts to level sensitive interrupts (I don't know
if it's the
reality or if it's due to an incomplete implementation - no datasheets
available to check) and use the fasteoi processing flow.
When entering the low level handler, level sensitive interrupts are
masked,
then eio'd in interrupt context and then unmasked at the end of hardirq
processing.
That's fine as any interrupt comming in-between will still be processed
since
the kernel replays those pending interrupts.
However, it appears that the eHEA interrupts are behaving as edge
sensitive
interrupts and are routed through the XICS which process those as level
sensitive using the fasteoi handler __OR__ the XICS loses interruptswhen
they
are masked.
Therefore the masking done in the handler causes any interrupt
happening while
in the handler to be lost.
So this patch maps the interrupts being requested through
ibmebus_request_irq() as edge sensitive interrupts (this concerns
both the eHEA
and the eHCA - only users of ibmebus_request_irq()) and changes the way
edge
interrupts are processed by the fasteoi handler.
It works for the eHEA, dunno for the eHCA.
So, unless all the designers of the XICS eHEA have been shot to keep
it
a secret, could someone knowledgeable shed some light on this issue.
Thanks,
Sebastien.
Not-Signed-off-by: Sebastien Dugue [EMAIL PROTECTED]
---
arch/powerpc/kernel/ibmebus.c | 11 ++-
kernel/irq/chip.c |5 +++--
kernel/irq/manage.c |9 ++---
3 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/kernel/ibmebus.c
b/arch/powerpc/kernel/ibmebus.c
index 9971159..5200323 100644
--- a/arch/powerpc/kernel/ibmebus.c
+++ b/arch/powerpc/kernel/ibmebus.c
@@ -41,6 +41,7 @@
#include linux/kobject.h
#include linux/dma-mapping.h
#include linux/interrupt.h
+#include linux/irq.h
#include linux/of.h
#include linux/of_platform.h
#include asm/ibmebus.h
@@ -213,11 +214,19 @@ int ibmebus_request_irq(u32 ist, irq_handler_t
handler,
void *dev_id)
{
unsigned int irq = irq_create_mapping(NULL, ist);
+ struct irq_desc *desc;
+ int ret;
if (irq == NO_IRQ)
return -EINVAL;
- return request_irq(irq, handler, irq_flags, devname, dev_id);
+ ret = request_irq(irq, handler, irq_flags, devname, dev_id);
+
+ desc = irq_desc + irq;
+ desc-status = ~(IRQ_TYPE_SENSE_MASK | IRQ_LEVEL);
+ desc-status |= IRQ_TYPE_EDGE_RISING;
+
+ return ret;
}
EXPORT_SYMBOL(ibmebus_request_irq);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index b7b397a..6d366ca 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -430,7 +430,7 @@ handle_fasteoi_irq(unsigned int irq, struct
irq_desc *desc)
action = desc-action;
if (unlikely(!action || (desc-status (IRQ_INPROGRESS |
IRQ_DISABLED {
- desc-status |= IRQ_PENDING;
+ desc-status |= IRQ_PENDING | IRQ_MASKED;
if (desc-chip-mask)
desc-chip-mask(irq);
goto out;
@@ -439,9 +439,10 @@ handle_fasteoi_irq(unsigned int irq, struct
irq_desc *desc)
desc-status |= IRQ_INPROGRESS;
/*
* In the threaded case we fall back to a mask+eoi sequence:
+* excepted for edge interrupts which are not masked.
*/
if (redirect_hardirq(desc)) {
- if (desc-chip-mask)
+ if (desc-chip-mask !(desc-status IRQ_TYPE_EDGE_BOTH))
desc-chip-mask(irq);
goto out;
}
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 3bffa20..3e39c71 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -788,9 +788,12 @@ static void do_hardirq(struct irq_desc *desc)
thread_simple_irq(desc);
else if (desc-handle_irq == handle_level_irq)
thread_level_irq(desc);
- else if (desc-handle_irq == handle_fasteoi_irq)
- thread_fasteoi_irq(desc);
- else if (desc-handle_irq == handle_edge_irq)
+ else if (desc-handle_irq == handle_fasteoi_irq) {
+ if (desc-status
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Hi,
we are a bit worried about putting this into the mainstream part of non real
time linux. There interrupts work perfectly fine, and it was a bit of a
challenge to get there for all cases / configurations / machines.
Could you try to enable these changes only for RT-Linux via a real-time
kconfig switch? This way we make sure we don't break the scheme for
eHEA / eHCA.
Regards,
Jan-Bernd, Christoph
Sebastien Dugue wrote:
WARNING: HACK - HACK - HACK
Under the RT kernel (with hardirq preemption) the eHEA driver hangs right
after booting. Fiddling with the hardirqs and softirqs priorities allows to
run a bit longer but as soon as the network gets under load, the hang
returns. After investigating, it appears that the driver is loosing interrupts.
To make a long story short, looking at the code, it appears that the XICS
maps all its interrupts to level sensitive interrupts (I don't know if it's the
reality or if it's due to an incomplete implementation - no datasheets
available to check) and use the fasteoi processing flow.
When entering the low level handler, level sensitive interrupts are masked,
then eio'd in interrupt context and then unmasked at the end of hardirq
processing.
That's fine as any interrupt comming in-between will still be processed since
the kernel replays those pending interrupts.
However, it appears that the eHEA interrupts are behaving as edge sensitive
interrupts and are routed through the XICS which process those as level
sensitive using the fasteoi handler __OR__ the XICS loses interrupts when they
are masked.
Therefore the masking done in the handler causes any interrupt happening while
in the handler to be lost.
So this patch maps the interrupts being requested through
ibmebus_request_irq() as edge sensitive interrupts (this concerns both the eHEA
and the eHCA - only users of ibmebus_request_irq()) and changes the way edge
interrupts are processed by the fasteoi handler.
It works for the eHEA, dunno for the eHCA.
So, unless all the designers of the XICS eHEA have been shot to keep it
a secret, could someone knowledgeable shed some light on this issue.
Thanks,
Sebastien.
Not-Signed-off-by: Sebastien Dugue [EMAIL PROTECTED]
---
arch/powerpc/kernel/ibmebus.c | 11 ++-
kernel/irq/chip.c |5 +++--
kernel/irq/manage.c |9 ++---
3 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/kernel/ibmebus.c b/arch/powerpc/kernel/ibmebus.c
index 9971159..5200323 100644
--- a/arch/powerpc/kernel/ibmebus.c
+++ b/arch/powerpc/kernel/ibmebus.c
@@ -41,6 +41,7 @@
#include linux/kobject.h
#include linux/dma-mapping.h
#include linux/interrupt.h
+#include linux/irq.h
#include linux/of.h
#include linux/of_platform.h
#include asm/ibmebus.h
@@ -213,11 +214,19 @@ int ibmebus_request_irq(u32 ist, irq_handler_t handler,
void *dev_id)
{
unsigned int irq = irq_create_mapping(NULL, ist);
+ struct irq_desc *desc;
+ int ret;
if (irq == NO_IRQ)
return -EINVAL;
- return request_irq(irq, handler, irq_flags, devname, dev_id);
+ ret = request_irq(irq, handler, irq_flags, devname, dev_id);
+
+ desc = irq_desc + irq;
+ desc-status = ~(IRQ_TYPE_SENSE_MASK | IRQ_LEVEL);
+ desc-status |= IRQ_TYPE_EDGE_RISING;
+
+ return ret;
}
EXPORT_SYMBOL(ibmebus_request_irq);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index b7b397a..6d366ca 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -430,7 +430,7 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc)
action = desc-action;
if (unlikely(!action || (desc-status (IRQ_INPROGRESS |
IRQ_DISABLED {
- desc-status |= IRQ_PENDING;
+ desc-status |= IRQ_PENDING | IRQ_MASKED;
if (desc-chip-mask)
desc-chip-mask(irq);
goto out;
@@ -439,9 +439,10 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc)
desc-status |= IRQ_INPROGRESS;
/*
* In the threaded case we fall back to a mask+eoi sequence:
+* excepted for edge interrupts which are not masked.
*/
if (redirect_hardirq(desc)) {
- if (desc-chip-mask)
+ if (desc-chip-mask !(desc-status IRQ_TYPE_EDGE_BOTH))
desc-chip-mask(irq);
goto out;
}
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 3bffa20..3e39c71 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -788,9 +788,12 @@ static void do_hardirq(struct irq_desc *desc)
thread_simple_irq(desc);
else if (desc-handle_irq == handle_level_irq)
thread_level_irq(desc);
- else if (desc-handle_irq == handle_fasteoi_irq)
- thread_fasteoi_irq(desc);
- else if (desc-handle_irq == handle_edge_irq)
+ else
Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
Hi Thomas, Jan-Bernd, Christoph,
On Mon, 15 Sep 2008 14:35:16 +0200 Thomas Klein [EMAIL PROTECTED] wrote:
Hi,
we are a bit worried about putting this into the mainstream part of non real
time linux.
Heck, I sure do not want this to be applied mainstream nor into any tree.
The sole purpose of this patch was to trigger some reaction from the people who
know the hardware and try to understand where the problem lies.
There interrupts work perfectly fine, and it was a bit of a
challenge to get there for all cases / configurations / machines.
Agreed, but the fact that it fails with hardirq preemption leads me to
believe (without any more knowledge about the harware) that there might be
something amiss with this driver (or the code concerning the XICS)
nevertheless.
Could you try to enable these changes only for RT-Linux via a real-time
kconfig switch?
Nope, this is just a quick hack that allows me to have a functional eHEA under
the rt kernel. I want to understand what the problem is:
- Is the eHEA really delivering level interrupts to the XICS?
- Is the XICS loosing interrupts when they are masked?
- ...?
This way we make sure we don't break the scheme for
eHEA / eHCA.
Sure, I do not want to break anything, quite the opposite in fact ;-)
Thanks,
Sebastien.
Regards,
Jan-Bernd, Christoph
Sebastien Dugue wrote:
WARNING: HACK - HACK - HACK
Under the RT kernel (with hardirq preemption) the eHEA driver hangs right
after booting. Fiddling with the hardirqs and softirqs priorities allows to
run a bit longer but as soon as the network gets under load, the hang
returns. After investigating, it appears that the driver is loosing
interrupts.
To make a long story short, looking at the code, it appears that the XICS
maps all its interrupts to level sensitive interrupts (I don't know if it's
the
reality or if it's due to an incomplete implementation - no datasheets
available to check) and use the fasteoi processing flow.
When entering the low level handler, level sensitive interrupts are
masked,
then eio'd in interrupt context and then unmasked at the end of hardirq
processing.
That's fine as any interrupt comming in-between will still be processed
since
the kernel replays those pending interrupts.
However, it appears that the eHEA interrupts are behaving as edge
sensitive
interrupts and are routed through the XICS which process those as level
sensitive using the fasteoi handler __OR__ the XICS loses interrupts when
they
are masked.
Therefore the masking done in the handler causes any interrupt happening
while
in the handler to be lost.
So this patch maps the interrupts being requested through
ibmebus_request_irq() as edge sensitive interrupts (this concerns both the
eHEA
and the eHCA - only users of ibmebus_request_irq()) and changes the way edge
interrupts are processed by the fasteoi handler.
It works for the eHEA, dunno for the eHCA.
So, unless all the designers of the XICS eHEA have been shot to keep it
a secret, could someone knowledgeable shed some light on this issue.
Thanks,
Sebastien.
Not-Signed-off-by: Sebastien Dugue [EMAIL PROTECTED]
---
arch/powerpc/kernel/ibmebus.c | 11 ++-
kernel/irq/chip.c |5 +++--
kernel/irq/manage.c |9 ++---
3 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/kernel/ibmebus.c b/arch/powerpc/kernel/ibmebus.c
index 9971159..5200323 100644
--- a/arch/powerpc/kernel/ibmebus.c
+++ b/arch/powerpc/kernel/ibmebus.c
@@ -41,6 +41,7 @@
#include linux/kobject.h
#include linux/dma-mapping.h
#include linux/interrupt.h
+#include linux/irq.h
#include linux/of.h
#include linux/of_platform.h
#include asm/ibmebus.h
@@ -213,11 +214,19 @@ int ibmebus_request_irq(u32 ist, irq_handler_t
handler,
void *dev_id)
{
unsigned int irq = irq_create_mapping(NULL, ist);
+ struct irq_desc *desc;
+ int ret;
if (irq == NO_IRQ)
return -EINVAL;
- return request_irq(irq, handler, irq_flags, devname, dev_id);
+ ret = request_irq(irq, handler, irq_flags, devname, dev_id);
+
+ desc = irq_desc + irq;
+ desc-status = ~(IRQ_TYPE_SENSE_MASK | IRQ_LEVEL);
+ desc-status |= IRQ_TYPE_EDGE_RISING;
+
+ return ret;
}
EXPORT_SYMBOL(ibmebus_request_irq);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index b7b397a..6d366ca 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -430,7 +430,7 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc
*desc)
action = desc-action;
if (unlikely(!action || (desc-status (IRQ_INPROGRESS |
IRQ_DISABLED {
- desc-status |= IRQ_PENDING;
+ desc-status |= IRQ_PENDING | IRQ_MASKED;
