From: Noah Goldstein <goldstein.w.n@gmail.com>
To: unlisted-recipients:; (no To-header on input)
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
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: Mon, 27 Sep 2021 13:02:34 -0500 [thread overview]
Message-ID: <CAFUsyfJWXJEc1879uX_YOJg7cvie0gitv+bu83DiUXiE74uQww@mail.gmail.com> (raw)
In-Reply-To: <20210920053951.4093668-1-goldstein.w.n@gmail.com>
On Mon, Sep 20, 2021 at 12:40 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> This commit creates a new mask, XFEATURE_MASK_ZMM, to test against
> xfeatures for conditionally updating the axx512_timestamp.
>
> Based on the comments, the avx512 state is meant to track when the
> state would cause frequencey throttling. The opmasks (k0-k7) do not
> cause frequency throttling, so they don't make sense to include.
>
> The current implementation, as well as the old, still does have a
> false positive on ymm16-ymm31 and xmm16-31 because
> XFEATURE_MASK_Hi16_ZMM includes them.
>
> Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> ---
> Issue is reproducible with the following code on x86_64:
>
> ```
> .global _start
> .text
> _start:
> korq %k0, %k0, %k0
>
> loop:
> jmp loop
>
>
> movl $60, %eax
> xorl %edi, %edi
> syscall
> ```
>
> Pretending run as executable named "foo":
>
> $> cat /proc/$(pidof foo)/arch_status
>
>
> This should yield -1 as no frequency changing AVX512 instructions
> where used but instead tracks the process.
>
> Note there still is a false positive with ymm16-ymm31 and xmm16-xmm31
> but since there is no state to distinguish between there use and
> zmm16-31 that seems inevitable.
>
>
> arch/x86/include/asm/fpu/types.h | 2 ++
> arch/x86/kernel/fpu/core.c | 4 +++-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> index f5a38a5f3ae1..a4816fa7d541 100644
> --- a/arch/x86/include/asm/fpu/types.h
> +++ b/arch/x86/include/asm/fpu/types.h
> @@ -141,6 +141,8 @@ enum xfeature {
> #define XFEATURE_MASK_AVX512 (XFEATURE_MASK_OPMASK \
> | XFEATURE_MASK_ZMM_Hi256 \
> | XFEATURE_MASK_Hi16_ZMM)
> +#define XFEATURE_MASK_ZMM (XFEATURE_MASK_ZMM_Hi256 \
> + | XFEATURE_MASK_Hi16_ZMM)
>
> #define FIRST_EXTENDED_XFEATURE XFEATURE_YMM
>
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index 7ada7bd03a32..342620a2e8ef 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -104,8 +104,10 @@ void save_fpregs_to_fpstate(struct fpu *fpu)
> /*
> * AVX512 state is tracked here because its use is
> * known to slow the max clock speed of the core.
> + * Note: This has a false positive on Hi16 ymm and
> + * xmm registers.
> */
> - if (fpu->state.xsave.header.xfeatures & XFEATURE_MASK_AVX512)
> + if (fpu->state.xsave.header.xfeatures & XFEATURE_MASK_ZMM)
> fpu->avx512_timestamp = jiffies;
> return;
> }
> --
> 2.25.1
>
Ping
(sorry if this has shown up multiple times for anyone,
was accidentally including HTML earlier)
next prev parent reply other threads:[~2021-09-27 18:02 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 [this message]
2021-10-13 22:36 ` Noah Goldstein
2021-10-14 8:28 ` Borislav Petkov
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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