Hello, I tried the patch and it applies to 2.6.28 (with some offsets). I guess that it perfectly works for 2.6.29.
Thank you, Victor On Thu, May 28, 2009 at 9:54 AM, stephane eranian <eran...@googlemail.com> wrote: > Victor, > > Your patch was applied with a tiny change to use for_each_bit(). > Please try it again. > Thanks. > > On Thu, May 21, 2009 at 1:20 AM, victor jimenez <betaband...@gmail.com> wrote: >> Hello, >> >> the program I was using when I discovered the problem is pretty >> complex, but I will try to see if I can make a small test program >> which can reproduce the error. >> >> In the meanwhile, I have created a very small patch which can fix the >> problem. I am attaching it. It tries to emulate the Intel behaviour >> when stopping (i.e., PMDs are saved). >> >> Do you think it is OK? >> >> Regards, >> Victor >> >> On Wed, May 20, 2009 at 7:44 PM, Corey J Ashford <cjash...@us.ibm.com> wrote: >>> victor jimenez <betaband...@gmail.com> wrote on 05/20/2009 09:24:43 AM: >>> >>>> Hello, >>>> >>>> I did more tests and I think I found the reason why it is not working. >>>> I am attaching a log with the debug information. The log shows >>>> information between a call to sys_pfm_start() and sys_pfm_stop(), plus >>>> a following call to sys_pfm_read_pmds(). >>>> >>>> In file perfmon/perfmon_ctxsw.c:242, pfm_save_pmds() is called >>>> depending on the value returned by pfm_arch_ctxswout_thread(). This >>>> second function returns the value returned by pfm_arch_is_active(). >>>> pfm_arch_is_active() returns 1 when the process is being monitor >>>> (after calling pfm_start) and 0 if the process is not (after calling >>>> pfm_stop). >>>> >>>> The problem is that using only pfm_arch_is_active() to determine >>>> whether we should save the PMDs or not is not enough. When pfm_stop() >>>> is called the PMDs are not being saved in the powerpc implementation >>>> of perfmon2 (they are saved in the x86 implementation). Therefore, if >>>> after calling pfm_stop() a the process is switched out >>>> pfm_arch_is_active() will return 0 (because the process is not being >>>> monitored; we already call pfm_stop()). This will cause that the PMDs >>>> are not saved at the context switch time and, thus the wrong ones will >>>> be restored later. >>>> >>>> All this can be seen in the attached log. At line 103 sys_pfm_stop() >>>> is called. At line 112 sys_pfm_read_pmds() is called. For instance, >>>> the value for counter 5 (#instructions) is 1218670811. Then a context >>>> switch comes, but at line 128 we can see how need_save_pmds is 0 so >>>> the PMDs are not saved. Next time they are restored, at line 135 (for >>>> counter 5) the value is 1207034044. This value is the value which was >>>> saved before at line 83. >>>> >>>> I hope this can help to find an solution. >>> >>> >>> It definitely does! I haven't looked at this code for awhile, so I'm >>> working on getting back up to speed. I see the exact issue you are >>> talking about and how the Power implementation is different from the x86 >>> implementation. The structure of the calls is different: x86 has a >>> stop_save per-pmu-type call, whereas Power has a single pfm_stop_active >>> call. You can see that the comments in the Power code originally came >>> from the x86 implementation, because it still refers to "stop_save()" in >>> pfm_arch_stop, but obviously we took a slightly different tack after the >>> two diverged. >>> >>> I think the fix needs to go in pfm_stop_active, though, since that is the >>> equivalent spot in the Power implementation. I will try out a fix and see >>> how it goes. >>> >>> Do you have a test case I could try that reproduces this? If not, I'm >>> sure >>> I could come up with one, but a ready-made test case would save me some >>> time. >>> >>> >>> Regards, >>> >>> - Corey >>> >>> Corey Ashford >>> Software Engineer >>> IBM Linux Technology Center, Linux Toolchain >>> cjash...@us.ibm.com >>> >>> >> >> ------------------------------------------------------------------------------ >> Register Now for Creativity and Technology (CaT), June 3rd, NYC. CaT >> is a gathering of tech-side developers & brand creativity professionals. 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