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Re: [PATCH] X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Wed, 24 Aug 2016 08:23:20 -0700
- Subject: Re: [PATCH] X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOojpuFz1jTbMpNcqZK1KVDqaWozNuEuS3E67dvD3Rh=hw@mail.gmail.com> <c6e21847-bc95-3c75-ed54-798c62194072@redhat.com>
On Wed, Aug 24, 2016 at 3:55 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 08/23/2016 11:53 PM, H.J. Lu wrote:
>>
>> Tested on x86-64 with/without AVX/AVX512. OK for master?
>
>
> Is this supposed to address a performance issue in actually shipping
> silicon?
We only see this performance issue with SSE AES instructions on
AVX512 machines with XGETBV (ECX == 1) and my patch fixes it.
Other AVX machines and other SSE instructions are OK.
> It seems there are implementations out there which support AVX-512F and
> XSAVEOPT, but not the XGETBV functionality required by this patch.
Knights Landing doesn't have this performance issue.
--
H.J.