linux-kernel - Re: [RFC PATCH 00/10] x86: Allocate AVX512 xstate ondemand

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Message-ID: <20211204115545.GW16608@worktop.programming.kicks-ass.net>
Date:   Sat, 4 Dec 2021 12:55:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        chang.seok.bae@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/10] x86: Allocate AVX512 xstate ondemand

On Fri, Dec 03, 2021 at 12:36:26AM +0000, Jiaxun Yang wrote:
> This series makes allocation of AVX512 xstate buffer ondemand.
> It can save some memory (~2k for a thread not using AVX512).
> 
> Also we are going to have heterogeneous processors that
> only some cores support AVX512, it can be helpful when
> dealing with such processors.
> 
> Patch 1~6 are some preparations.
> Patch 7 moves reallocation of xstate buffer to save_fpregs_to_fpstate.
> Patch 8~10 are some cleanup and enablement work.
> 
> Tested on a Skylake-X system with AVX512 intensive y-cruncher and numpy,
> the performance impact seems neglectable.
> 
> Any sugguestions are welcomed.

If we're going to do asymmetric avx512 it needs to come with a prctl()
interface like AMX.