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Date: Thu, 25 Jun 2009 12:39:23 +0200 From: stephane eranian <eranian@...glemail.com> To: Ingo Molnar <mingo@...e.hu> Cc: Yong Wang <yong.y.wang@...ux.intel.com>, "Wang, Yong Y" <yong.y.wang@...el.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, LKML <linux-kernel@...r.kernel.org>, Paul Mackerras <paulus@...ba.org>, Andi Kleen <andi@...stfloor.org> Subject: Re: perf_counter Atom patch On Wed, Jun 24, 2009 at 10:52 AM, Ingo Molnar<mingo@...e.hu> wrote: > > * Yong Wang <yong.y.wang@...ux.intel.com> wrote: > >> On Tue, Jun 23, 2009 at 11:47:17AM +0200, Ingo Molnar wrote: >> > >> > * Yong Wang <yong.y.wang@...ux.intel.com> wrote: >> > >> > > On Tue, Jun 23, 2009 at 10:40:45AM +0200, stephane eranian wrote: >> > > > Yong, >> > > > >> > > > On Tue, Jun 23, 2009 at 10:27 AM, stephane >> > > > eranian<eranian@...glemail.com> wrote: >> > > > > Hi, >> > > > > >> > > > > On Tue, Jun 23, 2009 at 9:59 AM, Yong Wang<yong.y.wang@...ux.intel.com> wrote: >> > > > >> On Tue, Jun 23, 2009 at 09:45:03AM +0200, stephane eranian wrote: >> > > > >>> >> > > > >>> Unfortunately, I don't have a N270 to compare with your results. >> > > > >>> We need to verify whether or not N270 implements the fixed counters. >> > > > >>> Does it report architected perfmon v3 or v1? >> > > > >>> >> > > > >> >> > > > >> All Atom processors report perfmon v3 as specified in SDM. N270 is no >> > > > >> exception. >> > > > >> >> > > > > V3 does not set a minimal number of fixed counters, could be zero. But >> > > > > that seems >> > > > > odd. Let me ask around. >> > > > > >> > > > Second thought on this: >> > > > x86_pmu.num_counters_fixed = >> > > > max((int)edx.split.num_counters_fixed, 3); >> > > > >> > > > rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, x86_pmu.intel_ctrl); >> > > > >> > > > >> > > > Forcing num_counter_fixed is not enough, you need to make sure >> > > > they are actually activated in GLOBAL_CTRL, i.e., make sure bits >> > > > 32-34 are set in intel_ctrl. Depending on which machine you're >> > > > on, the power on value for GLOBAL_CTRL changes. The correct >> > > > value for it should be that ONLY generic counters are on by >> > > > default. >> > > > >> > > >> > > Oh, this might be why fixed counter do not work on my Atom box. I >> > > will look into it. [...] >> > >> > Thanks - having a different bootup default for the global ctrl >> > indeed sounds like a good and plausible explanation - please send a >> > patch for that if you've tested it, removing that quirk and adding >> > the global-enable ctrl logic. >> > >> >> The root cause of fixed counters not working on Atom is indeed >> related to global counter control MSR. The power-on value on Atom >> is 0x3 which means only general purpose counters are enabled by >> default. The power-on value on Core2 is 0xffffffffffffffff which I >> believe is also the case for Nehalem. That's why Core2 and Nehalem >> do not have the problem. > > I suspect it can also be firmware/BIOS and microcode version > dependent - it's better to not rely on bootup state like that > indeed. I would recommend you ignore boot up values and setup GLOBAL_CTRL* the way you need. So I agree. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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