That's great news, Stephane, thanks! I'll give this a whirl on Monday. - Corey
On 08/29/2009 10:00 AM, stephane eranian wrote: > Corey, > > I think I have found and fixed the problem. As I was debugging > 2.6.30 on Itanium I found a couple of issues. One of them is > identical to the one you reported. > > > It turns out that: >>> if (!test_thread_flag(TIF_PERFMON_CTXSW)) >>> goto skip_all; > Is bogus because current is not the task we want to test on. > It needs to be as follows instead: > >>> if (!test_tsk_thread_flag(task, TIF_PERFMON_CTXSW)) >>> goto skip_all; > > With that, I think Power should work again. > > I have also fixed a bogus initialization on set0. But that was > inttroduced just last week by my vmalloc() changes. > > On Fri, Aug 28, 2009 at 3:54 PM, stephane eranian<eran...@googlemail.com> > wrote: >> Corey, >> >> On Fri, Aug 28, 2009 at 3:05 AM, Corey >> Ashford<cjash...@linux.vnet.ibm.com> wrote: >>> Hi Stephane, >>> >>> I have made some progress in tracking this problem down. The big picture is >>> that pfm_arch_ctxswin_thread is never getting called, so when the thread is >>> switched out, and then back in again at some point, the PMU context is not >>> getting restored onto the PMU registers, causing the counters to stop till >>> the end of the run. >>> >>> pfm_arch_ctxswin_thread is not getting called because of the following code >>> in perfmon_ctxsw.c: >>> /* >>> * TIF flag was removed since switch_to >>> * context is detaching, skip everything, >>> * keep oncpu=-1 >>> */ >>> if (!test_thread_flag(TIF_PERFMON_CTXSW)) >>> goto skip_all; >>> >>> Apparently the TIF_PERFMON_CTXSW flag is always cleared. I haven't tracked >>> any farther back than this yet, but was hoping this might trigger a thought >>> or two in your mind as to what might be going on. >>> >> >> TIF_PERFMON_CTXSW is only set in pfm_preload_context(). If you are testing >> with self.c I don't see how this can be happening at this point. I >> think you have >> to instrument the places where the flag gets cleared. >> >> >> >>> I also noticed that this code appears to have changed from 2.6.29 to 2.6.30. >>> >>> Anyway, I'd appreciate any thoughts you might have on this. I may not get >>> back to looking at this till Monday afternoon, so no huge rush. >>> >>> Thanks for your consideration, >>> >>> - Corey >>> >>> stephane eranian wrote: >>>> >>>> Corey, >>>> >>>> On Wed, Aug 26, 2009 at 1:55 AM, Corey >>>> Ashford<cjash...@linux.vnet.ibm.com> wrote: >>>>> >>>>> Corey Ashford wrote: >>>>>> >>>>>> stephane eranian wrote: >>>>>>> >>>>>>> On Mon, Aug 24, 2009 at 8:48 PM, Corey >>>>>>> Ashford<cjash...@linux.vnet.ibm.com> wrote: >>>>>>>> >>>>>>>> stephane eranian wrote: >>>>>>>>> >>>>>>>>> Corey, >>>>>>>>> >>>>>>>> [snip] >>>>>>>>> >>>>>>>>> Here are a couple of tests you could try and run to narrow it down: >>>>>>>>> - taskset -c 0 self >>>>>>>>> - syst >>>>>>>>> >>>>>>>> "taskset -c 0 self" doesn't improve the behavior. The results are >>>>>>>> still >>>>>>>> all >>>>>>>> over the place. >>>>>>>> >>>>>>> That's strange, must be something really central. >>>>>>> You need to enable debugging. Careful as this has changed again in >>>>>>> 2.6.30 >>>>>>> because of the dynamic_printk stuff. The good thing is that now you can >>>>>>> turn on/off individual printk. >>>>>> >>>>>> I'm not familiar with dynamic_printk, so that will take some research. >>>>>> >>>>>>>> "syst" is giving me an error, which may be something completely >>>>>>>> unrelated: >>>>>>>> >>>>>>>> [r...@elm3c4 examples_v2.x]# ./syst >>>>>>>> cannot set affinity to CPU0: Invalid argument >>>>>>>> >>>>>>> Weird. You have a CPU0, don't you? >>>>>> >>>>>> Yes :) I'm still debugging this to figure out what's going on. No >>>>>> results yet >>>>>> (took me awhile to get systemtap running due to many pilot errors) >>>>> >>>>> Ok, I tracked the syst problem down. There is an error in syst.c which >>>>> manifests itself on big-endian machines when syst.c is compiled in 32-bit >>>>> mode. >>>>> >>>>> The bit vector which is used to describe the cpus that you want to set >>>>> the >>>>> affinity for is an array of 32-bit words (when using the >>>>> compat_sys_sched_setaffinity system call in 32-bit mode). syst programs >>>>> a >>>>> vector of 64-bit words. On a little endian machine, this wouldn't >>>>> matter, >>>>> because the least significant byte of the 32-bit or 64-bit word is always >>>>> at >>>>> offset 0. But on a big-endian machine, the least significant byte is at >>>>> offset 0x3 or 0x7 depending on the word size. So the result is that the >>>>> bit >>>>> vector is interpreted as setting the affinity for a cpu which does not >>>>> exist. >>>>> >>>> I think nowdays, we should simply use the libc cpu_set and call the >>>> regular sched_setaffinity() instead of having a custom version. That >>>> was from a long time ago. Hopefully, the official API will work on 32-bit >>>> big-endian systems. >>>> >>>>> There are a couple of ways to fix this, and I will post a patch which >>>>> contains both versions. >>>>> >>>>> So, after fixing this problem, syst does produce reliable results on >>>>> 2.6.30. >>>>> So I am assuming now that this the problem with the self test (and >>>>> others) >>>>> is that something is messed up with the per-thread context code. >>>>> >>>> Yes, most likely. That is why I asked you to try taskset -c 0 self to >>>> avoid >>>> switching from one CPU to another. But obviously you can be switched in >>>> and out. >>>> >>>> >>>>> I will be start working on this. >>>>> >>>>> - Corey >>>>> >>>>> >>> >>> -- >>> Regards, >>> >>> - Corey >>> >>> Corey Ashford >>> Software Engineer >>> IBM Linux Technology Center, Linux Toolchain >>> Beaverton, OR >>> 503-578-3507 >>> cjash...@us.ibm.com >>> >> ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
