On 2012-04-02 22:41, Gilles Chanteperdrix wrote: > On 04/02/2012 05:54 PM, Jan Kiszka wrote: >> On 2012-04-02 17:39, Gilles Chanteperdrix wrote: >>> On 02/24/2012 03:40 PM, Philippe Gerum wrote: >>>> On 02/24/2012 01:28 PM, Gilles Chanteperdrix wrote: >>>>> On 02/20/2012 05:46 PM, Philippe Gerum wrote: >>>>>> On 02/19/2012 08:43 PM, Gilles Chanteperdrix wrote: >>>>>>> >>>>>>> Hi, >>>>>>> >>>>>>> restarting the ipipe-core is the good opportunity to look a bit at our >>>>>>> current state and think about what we could improve. On ARM, at least, >>>>>>> the thing we could improve is the timer subsystem. A long time ago, >>>>>>> linux has switched to a system allowing to select at run-time which >>>>>>> timer to use, and we do not really benefit from this, what timer we use >>>>>>> is selected at compile time, resulting in a massive ifdefery on arm, and >>>>>>> even on x86, we have to select at compile time whether using the 8254 or >>>>>>> APIC, whereas we could decide to use whatever linux is using, even say >>>>>>> HPET, without any compilation option. That is assuming we want to move >>>>>>> the x86 timer-specific code from xenomai to I-pipe. >>>>>>> >>>>>>> The idea to reach this goal would be to add some ipipe specific members >>>>>>> to the struct clock_event_device, the way we do for the interrupt >>>>>>> controller: >>>>>>> - a CLOCK_EVT_FEAT_IPIPE would signal that the clockevent device is >>>>>>> ipipe capable, meaning that it implements the following callback >>>>>>> - ipipe_steal would be called when stealing the timer, we could decide >>>>>>> to call this callback either as part of ipipe_request_timer, or with a >>>>>>> specific ipipe_steal_timer call, currently we simply set >>>>>>> __ipipe_mach_timerstolen to 1, but it is pure luck that we never needed >>>>>>> something more complicated, besides, we may want to start a timer that >>>>>>> was not started by linux so, we would put its initialization here; >>>>>>> - ipipe_stolen would record whether the timer is stolen >>>>>>> - ipipe_min_delta_ticks, ipipe_max_delta_ticks would be used by the >>>>>>> ipipe_set_next_event callback >>>>>>> - ipipe_ack would be called to ack the timer interrupt the way we >>>>>>> currently do it currently on arm with __ipipe_mach_acktimer >>>>>>> - ipipe_set_next_event would program the next timer shot, the way it is >>>>>>> currently done in __ipipe_mach_set_dec. >>>>>>> >>>>>>> All this is pretty straightforward, but there is still a question: how >>>>>>> does ipipe_request_timer select a timer. The idea is that on platform >>>>>>> without PIC muting, it is probably more efficient to use the same timer >>>>>>> for linux and xenomai. But on platforms with PIC muting, we could want >>>>>>> to select a different timer for linux and xenomai, but how do we find >>>>>>> it, what if linux has not selected a timer because it is unusable on >>>>>>> that platform? >>>>>> >>>>>> Checking the clock device mode for CLOCK_EVT_MODE_SHUTDOWN, and falling >>>>>> back to sharing the active kernel tick device + disabling PIC muting? >>>>> >>>>> OK. Another question is: do we want to move x86 timer handling from >>>>> xenomai to ipipe. If not, we have to find a way to support the two >>>>> possible configurations. What we could do is using the timer name in >>>>> ipipe_request_tickdev: if a timer name is supplied, we keep the old >>>>> implementation, if no timer name is supplied, we use the newho >>>>> implementation which looks for the best candidate with the >>>>> CLOCK_EVT_FEAT_IPIPE bit. >>>>> >>>>> >>>> >>>> Yes, makes sense. At any rate, handling the real-time timer the way we >>>> want for Xenomai directly from the pipeline is the only sane option. We >>>> only have to be careful about backward compatibility of the newest core >>>> pipelines with 2.6.x, until we stop maintaining this branch in favor of >>>> 3.x. We may also move ipipe_request_tckdev() to the compat module fully, >>>> removing it from the current API if that makes sense. >>>> >>> >>> For those who would like to follow, the result, a bit different from what >>> was originally planned is the interface implemented by this file: >>> http://git.xenomai.org/?p=ipipe-gch.git;a=blob;f=kernel/ipipe/timer.c;h=b9936469652d8fe998157d155fda77df81f0425a;hb=52d36aa86d5c5d463d86d384ad717f26ec96ef8c >>> >>> And ARM and x86 architectures were re-factored over this interface. As >>> an example, the implementation of x86 timers is in this patch: >>> http://git.xenomai.org/?p=ipipe-gch.git;a=commitdiff;h=52d36aa86d5c5d463d86d384ad717f26ec96ef8c;hp=675a8ed4365eb1f23b098f913caf40e4dc792b80 >>> >>> 8254, local APIC and HPET in legacy mode were tested, even selected >>> at run-time. Only per-cpu HPET remains to be tested (the hardware >>> I have does not support it). >> >> FWI, QEMU (w/ or w/o KVM) can emulated enough HPET timers, also with MSI >> support, but that was broken in I-pipe last time I checked. Use -global >> hpet.timers=4 (or more for more CPUs) and -global hpet.msi=on. > > No luck, I am using qemu 0.12.5, there is no -global option documented,
Err, that's prehistoric. Use stable 1.0.x at least to receive proper HPET support. > and these two values have no effect. Is there any way to have both the > kernel console directly in the terminal where qemu is launched, and a > way to stop qemu by hitting ctrl-C ? > > -serial stdio is what I want, but having -monitor stdio as well seems > impossible. -serial mon:stdio will establish a multiplexer between monitor and serial port on stdio. Switch between both via CTRL-A. Monitor commands stop & cont will control the guest execution. Also, if you want to debug your guest, use -s and gdb vmlinux / tar rem :1234. Jan
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