linux-kernel - Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

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Message-ID: <25f1cca7-fba7-63c1-f11d-17a3069a9ceb@intel.com>
Date:   Thu, 15 Apr 2021 10:00:25 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andy Lutomirski <luto@...nel.org>, Len Brown <lenb@...nel.org>
Cc:     Willy Tarreau <w@....eu>, Florian Weimer <fweimer@...hat.com>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-abi@...r.kernel.org,
        "libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
        Rich Felker <dalias@...c.org>, Kyle Huey <me@...ehuey.com>,
        Keno Fischer <keno@...iacomputing.com>
Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related
 features

On 4/15/21 9:24 AM, Andy Lutomirski wrote:
> In the patches, *as submitted*, if you trip the XFD #NM *once* and you
> are the only thread on the system to do so, you will eat the cost of a
> WRMSR on every subsequent context switch.

I think you're saying: If a thread trips XFD #NM *once*, every switch to
and from *that* thread will incur the WRMSR cost.

The first time I read this, I thought you were saying that all threads
would incur a WRMSR cost on every context switch.  If that's the case, I
grossly misread the patches. :)