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From:   Len Brown <lenb@kernel.org>
Date:   Fri, 21 May 2021 12:29:39 -0400
Message-ID: <CAJvTdK=suyVdH5U4WAdAmsJcnZbRx4tOot-Eu_SV4LSwLwP+zw@mail.gmail.com>
Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>, Willy Tarreau <w@1wt.eu>,
        Andy Lutomirski <luto@kernel.org>,
        "Bae, Chang Seok" <chang.seok.bae@intel.com>,
        Dave Hansen <dave.hansen@intel.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        "libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
        Rich Felker <dalias@libc.org>, Kyle Huey <me@kylehuey.com>,
        Keno Fischer <keno@juliacomputing.com>,
        Arjan van de Ven <arjan@linux.intel.com>
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On Mon, May 17, 2021 at 5:56 AM Florian Weimer <fweimer@redhat.com> wrote:

> How expensive is checking XCR0 via XGETBV instead, on the AMX path?

XGETBV takes about the same number of cycles as RDTSC (ie. it is
relatively fast)

Len Brown, Intel Open Source Technology Center