From: Noah Goldstein <goldstein.w.n@gmail.com>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: Adhemerval Zanella <adhemerval.zanella@linaro.org>,
"H.J. Lu" <hjl.tools@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v2] x86-64: Optimize bzero
Date: Thu, 10 Feb 2022 12:28:48 -0600 [thread overview]
Message-ID: <CAFUsyf+iiDUdNrHzs_3w5pYXTkm_UWm8noRWrXq829eHqKQiwg@mail.gmail.com> (raw)
In-Reply-To: <AS8PR08MB6534A0F2FCCDD5487CAE3F45832F9@AS8PR08MB6534.eurprd08.prod.outlook.com>
On Thu, Feb 10, 2022 at 7:02 AM Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
>
> Hi,
>
> >> The saving is in the lane-cross broadcast which is on the critical
> >> path for memsets in [VEC_SIZE, 2 * VEC_SIZE] (think 32-64).
>
> What is the speedup in eg. bench-memset? Generally the OoO engine will
> be able to hide a small increase in latency, so I'd be surprised it shows up
> as a significant gain.
>
> If you can show a good speedup in an important application (or benchmark
> like SPEC2017) then it may be worth pursuing. However there are other
> optimization opportunities that may be easier or give a larger benefit.
Very much so doubt any benefit on SPEC/other unless the compiler
decided to build zeros with long dependency chains instead of
xor.
>
> >> Agreed it's not clear if it's worth it to start replacing memset calls with
> >> bzero calls, but at the very least this will improve existing code that
> >> uses bzero.
>
> No code uses bzero, no compiler emits bzero. It died 2 decades ago...
>
> > My point is this is a lot of code and infrastructure for a symbol marked
> > as legacy for POSIX.1-2001 and removed on POSIX.1-2008 for the sake of
> > marginal gains in specific cases.
>
> Indeed, what we really should discuss is how to remove the last traces of
> bcopy and bcmp from GLIBC. Do we need to keep a compatibility symbol
> or could we just get rid of it altogether?
>
> Cheers,
> Wilco
next prev parent reply other threads:[~2022-02-10 18:29 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-08 22:43 H.J. Lu
2022-02-08 23:56 ` Noah Goldstein
2022-02-09 11:41 ` Adhemerval Zanella
2022-02-09 22:14 ` Noah Goldstein
2022-02-10 12:35 ` Adhemerval Zanella
2022-02-10 13:01 ` Wilco Dijkstra
2022-02-10 13:10 ` Adhemerval Zanella
2022-02-10 13:16 ` Adhemerval Zanella
2022-02-10 13:17 ` Wilco Dijkstra
2022-02-10 13:22 ` Adhemerval Zanella
2022-02-10 17:50 ` Alejandro Colomar (man-pages)
2022-02-10 19:19 ` Wilco Dijkstra
2022-02-10 20:27 ` Alejandro Colomar (man-pages)
2022-02-10 20:42 ` Adhemerval Zanella
2022-02-10 21:07 ` Patrick McGehearty
2022-02-11 13:01 ` Adhemerval Zanella
2022-02-12 23:46 ` Noah Goldstein
2022-02-14 12:07 ` Adhemerval Zanella
2022-02-14 12:41 ` Noah Goldstein
2022-02-14 14:07 ` Adhemerval Zanella
2022-02-14 15:03 ` H.J. Lu
2022-05-04 6:35 ` Sunil Pandey
2022-05-04 12:52 ` Adhemerval Zanella
2022-05-04 14:50 ` H.J. Lu
2022-05-04 14:54 ` Adhemerval Zanella
2022-02-10 22:00 ` Alejandro Colomar (man-pages)
2022-02-10 19:42 ` Adhemerval Zanella
2022-02-10 18:28 ` Noah Goldstein [this message]
2022-02-10 18:35 ` Noah Goldstein
2022-02-15 13:38 Wilco Dijkstra
2022-02-23 8:12 ` Noah Goldstein
2022-02-23 12:09 ` Adhemerval Zanella
2022-02-24 13:16 ` Wilco Dijkstra
2022-02-24 15:48 ` H.J. Lu
2022-02-24 22:58 ` Noah Goldstein
2022-02-24 23:21 ` Noah Goldstein
2022-02-25 17:37 ` Noah Goldstein
2022-02-25 13:51 ` Wilco Dijkstra
2022-02-25 17:35 ` Noah Goldstein
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