linux-kernel - Re: Why does glibc use AVX-512?

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Message-ID: <CAMe9rOp9S0A++Gf1hRoAL4tENk-xRk3yc=_Vx=V_+K63DOXspA@mail.gmail.com>
Date:   Fri, 26 Mar 2021 13:43:51 -0700
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     Florian Weimer <fw@...eb.enyo.de>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        "Carlos O'Donell" <carlos@...hat.com>,
        Rich Felker <dalias@...c.org>,
        libc-alpha <libc-alpha@...rceware.org>
Subject: Re: Why does glibc use AVX-512?

On Fri, Mar 26, 2021 at 1:35 PM Florian Weimer <fw@...eb.enyo.de> wrote:

>
> All this needs to work transparently without user intervention.  We
> cannot require firmware upgrades to fix the incorrect RTM reporting
> issue (the bug I referenced).  I think we can require software updates
> which tell glibc when to use RTM-enabled string functions if the
> dynamic selection does not work (either for performance reasons, or
> because of the RTM reporting bug).
>
> I want to avoid a situation where one in eight processes fail to work
> correctly because the CPUID checks ran on CPU 0, where RTM is reported
> as available, and then we trap when executing XTEST on other CPUs.

glibc can disable RTM based on CPU model and stepping.

-- 
H.J.