linux-kernel - Re: [RFC PATCH v2 1/4] tools/nolibc: x86-64: Use `rep movsb` for `memcpy()` and `memmove()`

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Message-ID: <4459ed19-f603-b4f6-392e-4e1322e06d56@gnuweeb.org>
Date:   Sat, 2 Sep 2023 19:36:47 +0700
From:   Ammar Faizi <ammarfaizi2@...weeb.org>
To:     Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>
Cc:     Willy Tarreau <w@....eu>,
        Thomas Weißschuh <linux@...ssschuh.net>,
        David Laight <David.Laight@...lab.com>,
        Nicholas Rosenberg <inori@...x.org>,
        Michael William Jonathan <moe@...weeb.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 1/4] tools/nolibc: x86-64: Use `rep movsb` for
 `memcpy()` and `memmove()`

On 2023/09/02 午後7:29, Alviro Iskandar Setiawan wrote:
> On Sat, Sep 2, 2023 at 1:38 PM Ammar Faizi wrote:
>> Ok, I'll do that.
> 
> Another micro-optimization. Since the likely case is the forward copy,
> make it the case that doesn't take the jump.
> 
> Pseudo C:
> if (unlikely(dst - src < n))
>          backward_copy();
> else
>          forward_copy();

Point taken.

-- 
Ammar Faizi