From: Sunil Pandey <skpgkp2@gmail.com>
To: Sunil Pandey <skpgkp2@gmail.com>,
Noah Goldstein <goldstein.w.n@gmail.com>,
Libc-stable Mailing List <libc-stable@sourceware.org>,
Hongjiu Lu <hjl.tools@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v5 2/2] x86: Optimize strlen-avx2.S
Date: Tue, 4 Oct 2022 18:10:51 -0700 [thread overview]
Message-ID: <CAMAf5_edt_W5-Dvv2GUitnB+wY+3G=j5e-CYUiOxPu6D8GGO3Q@mail.gmail.com> (raw)
In-Reply-To: <YzyjfhOkGAjWkQfz@aurel32.net>
On Tue, Oct 4, 2022 at 2:20 PM Aurelien Jarno <aurelien@aurel32.net> wrote:
>
> On 2022-09-28 06:54, Sunil Pandey via Libc-stable wrote:
> > Attached patch fixes BZ# 29611.
> >
> > I would like to backport it to 2.32,2.31,2.30,2.29 and 2.29. Let me know
> > if there is any objection.
>
> Sorry to be late on this. I have a few comments about that patch:
>
> > From 86e1d88e1a3c126597ef39165275ada7564cfce9 Mon Sep 17 00:00:00 2001
> > From: "H.J. Lu" <hjl.tools@gmail.com>
> > Date: Mon, 19 Apr 2021 10:45:07 -0700
> > Subject: [PATCH] x86-64: Require BMI2 for strchr-avx2.S
> >
> > Since strchr-avx2.S updated by
> >
> > commit 1f745ecc2109890886b161d4791e1406fdfc29b8
> > Author: noah <goldstein.w.n@gmail.com>
> > Date: Wed Feb 3 00:38:59 2021 -0500
> >
> > x86-64: Refactor and improve performance of strchr-avx2.S
> >
> > uses sarx:
> >
> > c4 e2 72 f7 c0 sarx %ecx,%eax,%eax
> >
> > for strchr-avx2 family functions, require BMI2 in ifunc-impl-list.c and
> > ifunc-avx2.h.
> >
> > (cherry picked from commit 83c5b368226c34a2f0a5287df40fc290b2b34359)
> > ---
> > sysdeps/x86_64/multiarch/ifunc-avx2.h | 4 ++--
> > sysdeps/x86_64/multiarch/ifunc-impl-list.c | 12 +++++++++---
> > 2 files changed, 11 insertions(+), 5 deletions(-)
>
> First of all 1f745ecc2109890886b161d4791e1406fdfc29b8 never got
> backported to 2.32 and older branches, and strchr-avx2.S in those
> branches do not use BMI2 instructions. So it doesn't make sense to
> backport it.
>
> That said the change in ifunc-avx2.h fixes:
>
> - memchr and rawmemchr, broken by the backport of acfd088a1963 ("x86:
> Optimize memchr-avx2.S")
> - strlen and strnlen, broken by the backport of aaa23c350715 ("x86:
> Optimize strlen-avx2.S")
>
> So the issues are fixed, but mostly by chance.
How do you know it is a "by chance" fix, do you have any evidence to back
your claim?
>
> NB: at this stage, I haven't verified the consistency of the ifunc
> selectors with ifunc-impl-list.c.
>
> --
> Aurelien Jarno GPG: 4096R/1DDD8C9B
> aurelien@aurel32.net http://www.aurel32.net
next prev parent reply other threads:[~2022-10-05 1:11 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210419233607.916848-1-goldstein.w.n@gmail.com>
[not found] ` <20210419233607.916848-2-goldstein.w.n@gmail.com>
[not found] ` <YzAO/ictPso/Y5LS@aurel32.net>
[not found] ` <CAFUsyf+U==grKgr9ZivEHDYsj=Xxi0MXBtQDfkU-JBHxb0pq+A@mail.gmail.com>
2022-09-28 13:54 ` Sunil Pandey
2022-09-28 14:02 ` Darren Tristano
2022-09-28 14:42 ` Noah Goldstein
2022-09-28 14:54 ` Sunil Pandey
2022-09-28 15:00 ` Noah Goldstein
2022-09-28 18:24 ` H.J. Lu
2022-09-30 13:19 ` FUCKETY FUCK FUCK FUCK - PLEASE FUCKING REMOVE ME> Darren Tristano
2022-09-28 18:23 ` [PATCH v5 2/2] x86: Optimize strlen-avx2.S H.J. Lu
2022-09-28 19:09 ` Sunil Pandey
2022-09-28 19:23 ` H.J. Lu
2022-09-30 13:19 ` FUCKETY FUCK FUCK FUCK - PLEASE FUCKING REMOVE ME> Darren Tristano
2022-10-04 21:19 ` [PATCH v5 2/2] x86: Optimize strlen-avx2.S Aurelien Jarno
2022-10-04 21:29 ` H.J. Lu
2022-10-05 1:10 ` Sunil Pandey [this message]
2022-10-05 14:23 ` Noah Goldstein
2022-10-05 16:35 ` Sunil Pandey
2022-10-05 17:11 ` Aurelien Jarno
2022-10-05 18:34 ` Sunil Pandey
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