From: Sunil Pandey <skpgkp2@gmail.com>
To: "Carlos O'Donell" <carlos@redhat.com>
Cc: libc-alpha@sourceware.org,
Adhemerval Zanella <adhemerval.zanella@linaro.org>,
hjl.tools@gmail.com
Subject: Re: [PATCH v2] x86_64: Optimize ffsll function code size.
Date: Wed, 24 Jan 2024 19:10:09 -0800 [thread overview]
Message-ID: <CAMAf5_cXK3Ee5X-Aak5TKMbXaA=bDKuCNAYFA_iMBrK_DMoyvg@mail.gmail.com> (raw)
In-Reply-To: <b0289e7d-6075-6631-b458-d63155b68e9e@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 1867 bytes --]
On Wed, Jan 10, 2024 at 11:19 AM Carlos O'Donell <carlos@redhat.com> wrote:
> On 7/31/23 14:35, Sunil K Pandey via Libc-alpha wrote:
> > Ffsll function size is 17 byte, this patch optimizes size to 16 byte.
> > Currently ffsll function randomly regress by ~20%, depending on how
> > code get aligned.
> >
> > This patch fixes ffsll function random performance regression.
>
> Here is my suggestion.
>
> Commit this to glibc 2.39 as an incremental improvement that we can
> backport
> to any active branch.
>
> I have already approved the removal for glibc 2.40 via Adhemerval's patch.
>
> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
>
> > Changes from v1:
> > - Further reduce size ffsll function size to 12 bytes.
> > ---
> > sysdeps/x86_64/ffsll.c | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/ffsll.c b/sysdeps/x86_64/ffsll.c
> > index a1c13d4906..6a5803c7c1 100644
> > --- a/sysdeps/x86_64/ffsll.c
> > +++ b/sysdeps/x86_64/ffsll.c
> > @@ -26,13 +26,13 @@ int
> > ffsll (long long int x)
> > {
> > long long int cnt;
> > - long long int tmp;
> >
> > - asm ("bsfq %2,%0\n" /* Count low bits in X and store
> in %1. */
> > - "cmoveq %1,%0\n" /* If number was zero, use -1 as
> result. */
> > - : "=&r" (cnt), "=r" (tmp) : "rm" (x), "1" (-1));
> > + asm ("mov $-1,%k0\n" /* Intialize CNT to -1. */
> > + "bsf %1,%0\n" /* Count low bits in X and store in CNT. */
> > + "inc %k0\n" /* Increment CNT by 1. */
> > + : "=&r" (cnt) : "r" (x));
> >
> > - return cnt + 1;
> > + return cnt;
> > }
> >
> > #ifndef __ILP32__
>
> --
> Cheers,
> Carlos.
>
I would like to backport this patch to release branches from 2.28 to 2.38.
Any comments or objections?
--Sunil
next prev parent reply other threads:[~2024-01-25 3:10 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-26 16:05 [PATCH] " Sunil K Pandey
2023-07-26 16:38 ` Richard Henderson
2023-07-26 16:50 ` H.J. Lu
2023-07-26 16:51 ` Noah Goldstein
2023-07-26 16:51 ` Sunil Pandey
2023-07-26 16:59 ` Noah Goldstein
2023-07-26 17:11 ` Adhemerval Zanella Netto
2023-07-27 0:31 ` Cristian Rodríguez
2023-07-26 20:43 ` Sunil Pandey
2023-07-26 21:05 ` Noah Goldstein
2023-07-26 22:37 ` Sunil Pandey
2023-07-27 0:00 ` Noah Goldstein
2023-07-27 8:16 ` Florian Weimer
2023-07-27 11:46 ` Alexander Monakov
2023-07-27 12:10 ` Florian Weimer
2023-07-27 13:59 ` Cristian Rodríguez
2023-07-27 14:00 ` Alexander Monakov
2023-07-27 15:13 ` Sunil Pandey
2023-07-27 15:50 ` Alexander Monakov
2023-07-27 16:24 ` Florian Weimer
2023-07-27 16:35 ` Adhemerval Zanella Netto
2023-07-27 17:09 ` Florian Weimer
2023-07-27 17:25 ` Sunil Pandey
2023-07-31 18:35 ` [PATCH v2] " Sunil K Pandey
2023-07-31 20:12 ` Adhemerval Zanella Netto
2023-07-31 20:58 ` Sunil Pandey
2023-07-31 22:57 ` Adhemerval Zanella Netto
2023-07-31 23:44 ` Sunil Pandey
2023-07-31 23:54 ` Noah Goldstein
2023-08-01 6:47 ` Andreas Schwab
2023-08-01 13:46 ` Adhemerval Zanella Netto
2023-08-01 18:25 ` Cristian Rodríguez
2024-01-10 19:19 ` Carlos O'Donell
2024-01-25 3:10 ` Sunil Pandey [this message]
2023-07-27 16:40 ` [PATCH] " Sunil Pandey
2023-07-26 17:04 ` Noah Goldstein
2023-07-26 17:25 ` Andrew Pinski
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