Re: Running Linux on FPGA
> On Jan 21 2007 00:14, Ralf Baechle wrote: > >On Sat, Jan 20, 2007 at 11:42:37PM +, sathesh babu wrote: > > > >> I am trying to run Linux-2.6.18.2 ( with preemption enable) > >> kernel on FPGA board which has MIPS24KE processor runs at 12 > >> MHZ. Programmed the timer to give interrupt at every 10msec. I > >> am seeing some inconsistence behavior during boot up processor. > >> Some times it stops after "NET: Registered protocol family 17" > >> and "VFS: Mounted root (jffs2 filesystem).". Could some give > >> some pointers why the behavior is random. Is it OK to program > >> the timer to 10 msec? or should it be more. > > > >The overhead of timer interrupts at this low clockrate is > >significant so I recommend to minimize the timer interrupt rate as > >far as possible. This is really a tradeoff between latency and > >overhead and matters much less on hardcores which run at hundreds of > >MHz. > > Hm I've been running 2.6.13 on a 10/20 MHz (switchable) i386 @ 100 Hz > before without any hangs during boot or operation. Interrupt service overhead varies a bit between architectures, but your observation isn't too surprising. While the 1000Hz Linux 2.6 default is just bad craziness for embedded cores and FPGA prototypes, I've only seen 100Hz be truly unusable for sub-megahertz hardware simulators, and then only when running virtual SMP kernels, where multiple virtual "CPUs" on the same core all had to perform timer interrupt service every clock interval, which multiplies the proportion of available cycles consumed. But even if the system boots and runs, it's pretty scary to look at the proportion of time that a 20MHz core spends in interrupt service with a HZ value of 100 or more. So on one hand I agree with Ralf that on slow systems, especially FPGA systems, one wants to keep the clock interrupt frequency down to no more than 100Hz as a general rule (less than 100 wouldn't compile on 2.6.9 without some minor patches, which took the minimum down to HZ=48, below which the various macros that depend on HZ start generating divide-by-zero problems), while on the other hand I agree with Jan that it's by no means certain that Satesh's problem is really one of too many clock interrupts. Regards, Kevin K. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
On Jan 21 2007 00:14, Ralf Baechle wrote: On Sat, Jan 20, 2007 at 11:42:37PM +, sathesh babu wrote: I am trying to run Linux-2.6.18.2 ( with preemption enable) kernel on FPGA board which has MIPS24KE processor runs at 12 MHZ. Programmed the timer to give interrupt at every 10msec. I am seeing some inconsistence behavior during boot up processor. Some times it stops after NET: Registered protocol family 17 and VFS: Mounted root (jffs2 filesystem).. Could some give some pointers why the behavior is random. Is it OK to program the timer to 10 msec? or should it be more. The overhead of timer interrupts at this low clockrate is significant so I recommend to minimize the timer interrupt rate as far as possible. This is really a tradeoff between latency and overhead and matters much less on hardcores which run at hundreds of MHz. Hm I've been running 2.6.13 on a 10/20 MHz (switchable) i386 @ 100 Hz before without any hangs during boot or operation. Interrupt service overhead varies a bit between architectures, but your observation isn't too surprising. While the 1000Hz Linux 2.6 default is just bad craziness for embedded cores and FPGA prototypes, I've only seen 100Hz be truly unusable for sub-megahertz hardware simulators, and then only when running virtual SMP kernels, where multiple virtual CPUs on the same core all had to perform timer interrupt service every clock interval, which multiplies the proportion of available cycles consumed. But even if the system boots and runs, it's pretty scary to look at the proportion of time that a 20MHz core spends in interrupt service with a HZ value of 100 or more. So on one hand I agree with Ralf that on slow systems, especially FPGA systems, one wants to keep the clock interrupt frequency down to no more than 100Hz as a general rule (less than 100 wouldn't compile on 2.6.9 without some minor patches, which took the minimum down to HZ=48, below which the various macros that depend on HZ start generating divide-by-zero problems), while on the other hand I agree with Jan that it's by no means certain that Satesh's problem is really one of too many clock interrupts. Regards, Kevin K. - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
On Jan 21 2007 00:14, Ralf Baechle wrote: >On Sat, Jan 20, 2007 at 11:42:37PM +, sathesh babu wrote: > >> I am trying to run Linux-2.6.18.2 ( with preemption enable) >> kernel on FPGA board which has MIPS24KE processor runs at 12 >> MHZ. Programmed the timer to give interrupt at every 10msec. I >> am seeing some inconsistence behavior during boot up processor. >> Some times it stops after "NET: Registered protocol family 17" >> and "VFS: Mounted root (jffs2 filesystem).". Could some give >> some pointers why the behavior is random. Is it OK to program >> the timer to 10 msec? or should it be more. > >The overhead of timer interrupts at this low clockrate is >significant so I recommend to minimize the timer interrupt rate as >far as possible. This is really a tradeoff between latency and >overhead and matters much less on hardcores which run at hundreds of >MHz. Hm I've been running 2.6.13 on a 10/20 MHz (switchable) i386 @ 100 Hz before without any hangs during boot or operation. -`J' -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
> > The overhead of timer interrupts at this low clockrate is significant > > so I recommend to minimize the timer interrupt rate as far as possible. > > This is really a tradeoff between latency and overhead and matters > > much less on hardcores which run at hundreds of MHz. For power sensitive > > applications lowering the interrupt rate can also help. And that's alredy > > pretty much what you need to know, that is a 10ms timer is fine. > > > > I have worked with FPGA Linux system which is reconfigurable > on-the-fly by the 200Mhz ARM9 CPU running Debian Linux, Altera Cyclone > II FPGA is included on my TS-7300 board. Advantage is, Altera FPGA and > a dedicated high-speed bus between the CPU and FPGA provides a good > design scope to provide many solutions. What's your point here? A 200MHz hard ore won't see the issues under discussion. We're talking about systems where the CPU itself is "soft" and implemented in an FPGA. Regards, Kevin K. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
On 1/21/07, Ralf Baechle <[EMAIL PROTECTED]> wrote: The overhead of timer interrupts at this low clockrate is significant so I recommend to minimize the timer interrupt rate as far as possible. This is really a tradeoff between latency and overhead and matters much less on hardcores which run at hundreds of MHz. For power sensitive applications lowering the interrupt rate can also help. And that's alredy pretty much what you need to know, that is a 10ms timer is fine. I have worked with FPGA Linux system which is reconfigurable on-the-fly by the 200Mhz ARM9 CPU running Debian Linux, Altera Cyclone II FPGA is included on my TS-7300 board. Advantage is, Altera FPGA and a dedicated high-speed bus between the CPU and FPGA provides a good design scope to provide many solutions. Coming to boot up (by an USB 1GB SD card), by doing enough software tuning bootup to a Linux prompt takes just 1.69 seconds after power-up. If I remember correctly, SD image will look at the state of jumper 6 (should be put ON), the full Debian bootup will be bypassed and the system will instead drop straight to a shell prompt. 1.69 seconds after power-on the serial console prompt is active and 2.41 seconds after power-on the video console is displayed. This software is based on Debian & has a vendor supplied Linux boot loader. Currently am working (slowly in free time) to bring the whole thing to FC6. Shall post the progres... Ralf ~Akula2 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
On 1/21/07, Ralf Baechle [EMAIL PROTECTED] wrote: The overhead of timer interrupts at this low clockrate is significant so I recommend to minimize the timer interrupt rate as far as possible. This is really a tradeoff between latency and overhead and matters much less on hardcores which run at hundreds of MHz. For power sensitive applications lowering the interrupt rate can also help. And that's alredy pretty much what you need to know, that is a 10ms timer is fine. I have worked with FPGA Linux system which is reconfigurable on-the-fly by the 200Mhz ARM9 CPU running Debian Linux, Altera Cyclone II FPGA is included on my TS-7300 board. Advantage is, Altera FPGA and a dedicated high-speed bus between the CPU and FPGA provides a good design scope to provide many solutions. Coming to boot up (by an USB 1GB SD card), by doing enough software tuning bootup to a Linux prompt takes just 1.69 seconds after power-up. If I remember correctly, SD image will look at the state of jumper 6 (should be put ON), the full Debian bootup will be bypassed and the system will instead drop straight to a shell prompt. 1.69 seconds after power-on the serial console prompt is active and 2.41 seconds after power-on the video console is displayed. This software is based on Debian has a vendor supplied Linux boot loader. Currently am working (slowly in free time) to bring the whole thing to FC6. Shall post the progres... Ralf ~Akula2 - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
The overhead of timer interrupts at this low clockrate is significant so I recommend to minimize the timer interrupt rate as far as possible. This is really a tradeoff between latency and overhead and matters much less on hardcores which run at hundreds of MHz. For power sensitive applications lowering the interrupt rate can also help. And that's alredy pretty much what you need to know, that is a 10ms timer is fine. I have worked with FPGA Linux system which is reconfigurable on-the-fly by the 200Mhz ARM9 CPU running Debian Linux, Altera Cyclone II FPGA is included on my TS-7300 board. Advantage is, Altera FPGA and a dedicated high-speed bus between the CPU and FPGA provides a good design scope to provide many solutions. What's your point here? A 200MHz hard ore won't see the issues under discussion. We're talking about systems where the CPU itself is soft and implemented in an FPGA. Regards, Kevin K. - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
On Jan 21 2007 00:14, Ralf Baechle wrote: On Sat, Jan 20, 2007 at 11:42:37PM +, sathesh babu wrote: I am trying to run Linux-2.6.18.2 ( with preemption enable) kernel on FPGA board which has MIPS24KE processor runs at 12 MHZ. Programmed the timer to give interrupt at every 10msec. I am seeing some inconsistence behavior during boot up processor. Some times it stops after NET: Registered protocol family 17 and VFS: Mounted root (jffs2 filesystem).. Could some give some pointers why the behavior is random. Is it OK to program the timer to 10 msec? or should it be more. The overhead of timer interrupts at this low clockrate is significant so I recommend to minimize the timer interrupt rate as far as possible. This is really a tradeoff between latency and overhead and matters much less on hardcores which run at hundreds of MHz. Hm I've been running 2.6.13 on a 10/20 MHz (switchable) i386 @ 100 Hz before without any hangs during boot or operation. -`J' -- - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
On Sat, Jan 20, 2007 at 11:42:37PM +, sathesh babu wrote: > Hi, > I am trying to run Linux-2.6.18.2 ( with preemption enable) kernel on FPGA > board which has MIPS24KE processor runs at 12 MHZ. Programmed the timer to > give interrupt at every 10msec. > I am seeing some inconsistence behavior during boot up processor. Some > times it stops after "NET: Registered protocol family 17" and "VFS: Mounted > root (jffs2 filesystem).". > Could some give some pointers why the behavior is random. > Is it OK to program the timer to 10 msec? or should it be more. The overhead of timer interrupts at this low clockrate is significant so I recommend to minimize the timer interrupt rate as far as possible. This is really a tradeoff between latency and overhead and matters much less on hardcores which run at hundreds of MHz. For power sensitive applications lowering the interrupt rate can also help. And that's alredy pretty much what you need to know, that is a 10ms timer is fine. Btw, is this coincidentally on a CoreFPGA 2 or 3 CPU card on a Malta board? Ralf - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Running Linux on FPGA
On Sat, Jan 20, 2007 at 11:42:37PM +, sathesh babu wrote: Hi, I am trying to run Linux-2.6.18.2 ( with preemption enable) kernel on FPGA board which has MIPS24KE processor runs at 12 MHZ. Programmed the timer to give interrupt at every 10msec. I am seeing some inconsistence behavior during boot up processor. Some times it stops after NET: Registered protocol family 17 and VFS: Mounted root (jffs2 filesystem).. Could some give some pointers why the behavior is random. Is it OK to program the timer to 10 msec? or should it be more. The overhead of timer interrupts at this low clockrate is significant so I recommend to minimize the timer interrupt rate as far as possible. This is really a tradeoff between latency and overhead and matters much less on hardcores which run at hundreds of MHz. For power sensitive applications lowering the interrupt rate can also help. And that's alredy pretty much what you need to know, that is a 10ms timer is fine. Btw, is this coincidentally on a CoreFPGA 2 or 3 CPU card on a Malta board? Ralf - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
