From: Ingo Molnar <mingo@elte.hu>
To: Borislav Petkov <bp@amd64.org>
Cc: Venki Pallipadi <venki@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Stephane Eranian <eranian@google.com>,
linux-kernel@vger.kernel.org, acme@redhat.com,
robert.richter@amd.com, eric.dumazet@gmail.com,
Andreas Herrmann <andreas.herrmann3@amd.com>
Subject: Re: [BUG] perf: perf sched warning possibly due to clock granularity on AMD
Date: Tue, 7 Feb 2012 10:50:00 +0100 [thread overview]
Message-ID: <20120207095000.GF15359@elte.hu> (raw)
In-Reply-To: <20120207090609.GB4852@aftab>
* Borislav Petkov <bp@amd64.org> wrote:
> On Tue, Feb 07, 2012 at 09:32:53AM +0100, Ingo Molnar wrote:
> > > Yes. If these two flags are set, TSC should be consistent and
> > > sched_clock_stable could be set and it will be reset if there
> > > is a call to mark_tsc_unstable().
> >
> > Most of the details swapped out from my brain meanwhile, but I
> > have some vague memories of a DMI quirk for some high-end system
> > that just did a sched_clock_stable = 0 or such.
> >
> > So if the common case is that the TSC is entirely synchronized
> > across CPUs, then we can default to that and rely on platform
> > initialization code or DMI quirks setting the few large-NUMA
> > systems to an unstable TSC.
>
> There's also 14be1f7454ea96ee614467a49cf018a1a383b189 which removed
> the setting of sched_clock_stable to 1 due to UV systems not being
> TSC-synchronized across blades.
>
> I guess, we could tentatively enable it on AMD provided nothing has
> marked the TSC as unstable already:
>
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index f4773f4..ddee619 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -456,6 +456,8 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
> if (c->x86_power & (1 << 8)) {
> set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
> set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
> + if (!check_tsc_unstable())
> + sched_clock_stable = 1;
> }
i'd go for that.
Thanks,
Ingo
next prev parent reply other threads:[~2012-02-07 9:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-06 13:25 [BUG] perf: perf sched warning possibly due to clock granularity on AMD Stephane Eranian
2012-02-06 14:26 ` Peter Zijlstra
2012-02-06 14:31 ` Stephane Eranian
2012-02-06 17:17 ` Arnaldo Carvalho de Melo
2012-02-06 15:34 ` Borislav Petkov
2012-02-06 16:37 ` Peter Zijlstra
2012-02-06 16:46 ` Borislav Petkov
2012-02-06 16:54 ` Peter Zijlstra
2012-02-06 20:27 ` Borislav Petkov
2012-02-06 20:31 ` Peter Zijlstra
2012-02-06 20:37 ` Borislav Petkov
2012-02-06 21:19 ` Venki Pallipadi
2012-02-07 7:51 ` Peter Zijlstra
2012-02-07 8:32 ` Ingo Molnar
2012-02-07 9:06 ` Borislav Petkov
2012-02-07 9:50 ` Ingo Molnar [this message]
2012-02-07 12:08 ` [PATCH] x86, AMD: Set sched_clock_stable Borislav Petkov
2012-02-15 15:30 ` Peter Zijlstra
2012-02-07 19:43 ` [tip:perf/core] x86/sched/perf/AMD: " tip-bot for Borislav Petkov
2012-02-08 15:07 ` [BUG] perf: perf sched warning possibly due to clock granularity on AMD Frederic Weisbecker
2012-02-08 15:10 ` Stephane Eranian
2012-02-08 15:22 ` Frederic Weisbecker
2012-02-08 15:23 ` Stephane Eranian
2012-02-18 16:50 ` [PATCH] perf tools: Fix ordering with unstable tsc Frederic Weisbecker
2012-02-22 15:35 ` Stephane Eranian
2012-02-22 15:39 ` David Ahern
2012-03-05 18:43 ` Frederic Weisbecker
2012-03-14 19:55 ` Arnaldo Carvalho de Melo
2012-03-14 20:07 ` David Ahern
2012-03-22 0:10 ` Frederic Weisbecker
2012-03-22 15:28 ` Arnaldo Carvalho de Melo
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