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From: Borislav Petkov <bp@alien8.de>
To: Noah Goldstein <goldstein.w.n@gmail.com>
Cc: tglx@linutronix.de, mingo@redhat.com, X86 ML <x86@kernel.org>,
	hpa@zytor.com, Andy Lutomirski <luto@kernel.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1] x86/fpu: Remove opmask state from avx512_timestamp check
Date: Thu, 14 Oct 2021 10:28:00 +0200	[thread overview]
Message-ID: <YWfqEIaCKOwSWGHF@zn.tnic> (raw)
In-Reply-To: <CAFUsyfJQ8_=QnZjZ2zS45wwB6AaRgL4JO8_sT1a_rXUsfh_1WQ@mail.gmail.com>

On Wed, Oct 13, 2021 at 05:36:14PM -0500, Noah Goldstein wrote:
> Ping2

Why?

The original patch which added this abomination:

2f7726f95557 ("x86/fpu: Track AVX-512 usage of tasks")

says already:

 the tracking mechanism is imprecise and can theoretically miss AVX-512
 usage during context switch. But it has been measured to be precise
 enough to be useful under real-world workloads like tensorflow and
 linpack.

 If higher precision is required, suggest user space tools to use the
 PMU-based mechanisms in combination.

and as you've noticed, the high 16 regs would cause a false positive
too.

So what is the actual real-life use case for this?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-10-14  8:28 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-20  5:39 [PATCH v1] x86/fpu: Remove opmask state from avx512_timestamp check Noah Goldstein
2021-09-27 18:02 ` Noah Goldstein
2021-10-13 22:36   ` Noah Goldstein
2021-10-14  8:28     ` Borislav Petkov [this message]
2021-10-14 15:49       ` Noah Goldstein
2021-10-15 14:40         ` Borislav Petkov
2021-10-15 15:25         ` Dave Hansen
2021-10-15 17:30           ` Noah Goldstein
2021-10-15 20:47 ` [PATCH v2 1/2] x86/fpu: Add helper function for tracking AVX512 status Noah Goldstein
2021-10-26 23:15   ` Noah Goldstein
2021-10-15 20:47 ` [PATCH v2 2/2] x86/xstate: Make AVX512 status tracking more accurate Noah Goldstein
2021-10-27 11:07   ` Borislav Petkov
2021-10-27 16:28     ` Noah Goldstein
2021-10-27 16:58       ` Borislav Petkov
2021-10-27 17:18         ` Noah Goldstein
2021-10-27 16:26 ` [PATCH v3 1/2] x86/fpu: Add helper function for tracking AVX512 status Noah Goldstein
2021-10-27 16:26   ` [PATCH v3 2/2] x86/xstate: Make AVX512 status tracking more accurate Noah Goldstein
2021-10-27 17:11     ` Borislav Petkov
2021-10-27 17:37       ` Noah Goldstein
2021-10-27 17:45         ` Borislav Petkov
2021-10-27 18:21           ` Noah Goldstein
2021-11-03 20:22             ` Noah Goldstein
2021-11-03 20:48               ` Borislav Petkov
2021-11-03 20:56                 ` Noah Goldstein
2021-10-27 17:17 ` [PATCH v4 1/2] x86/fpu: Add helper function for tracking AVX512 status Noah Goldstein
2021-10-27 17:17   ` [PATCH v4 2/2] x86/xstate: Make AVX512 status tracking more accurate Noah Goldstein
2021-10-27 18:21 ` [PATCH v5 1/2] x86/fpu: Add helper function for tracking AVX512 status Noah Goldstein
2021-10-27 18:21   ` [PATCH v5 2/2] x86/xstate: Make AVX512 status tracking more accurate Noah Goldstein
2021-11-16 16:21     ` [PATCH] x86/fpu: Correct AVX512 state tracking Borislav Petkov
2021-11-16 16:49       ` Noah Goldstein
2021-11-17 18:29 ` [tip: x86/fpu] " tip-bot2 for Noah Goldstein

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