linux-kernel - Re: [RFC PATCH] x86/CPU/AMD: Bring back Compute Unit ID

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Date:   Thu, 2 Feb 2017 18:04:56 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Ghannam, Yazen" <Yazen.Ghannam@....com>, x86-ml <x86@...nel.org>,
        Yves Dionne <yves.dionne@...il.com>,
        Brice Goglin <Brice.Goglin@...ia.fr>,
        Peter Zijlstra <peterz@...radead.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86/CPU/AMD: Bring back Compute Unit ID

On Thu, Feb 02, 2017 at 05:09:16PM +0100, Ingo Molnar wrote:
> If there's any doubt about the validity of the measurement I'd suggest doing:
> 
> 	perf stat -a --sync --repeat 3 ...
> 
> ... so that there's no perf overhead and skew from the many processes of a kernel 
> build workload, plus the --sync should reduce IO related noise.
> 
> Or:
> 
> 	perf stat --null --sync --repeat 3 ...
> 
> ... will only measure elapsed time, but will do that very precisely and with very 
> little overhead.

Yeah, I was talking to Peter about the -a thing on IRC... I think I'm going to
try that. Here's the full command I was using:

./tools/perf/perf stat -e task-clock,context-switches,cache-misses,cpu-migrations,page-faults,cycles,instructions,branches,branch-misses --repeat 3 --sync --pre ~/bin/pre-build-kernel.sh -- make -s -j17 bzImage

I think I stole it from you from some mail thread we had in the past.

-- 
Regards/Gruss,
    Boris.

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