Re: [PATCH] strbuf_write: omit system call when length is zero

From: Duy Nguyen <pclouds@gmail.com>
Date: Feb 26, 2016, 00:47 UTC
Message-ID: <CACsJy8DgjmdX681fRwB-JajPBRN+cNy=jFwEDW6D-dXhNi=_6g@mail.gmail.com>
In-Reply-To: <1456439678-5433-1-git-send-email-sbeller@google.com>

On Fri, Feb 26, 2016 at 5:34 AM, Stefan Beller <sbeller@google.com> wrote:

> In case the length of the buffer is zero, we do not need to call the
> fwrite system call as a performance improvement.

fwrite is a libc call, not system call. Are you sure it always calls write() (assuming buffering is off)?

Show 39 quoted lines

>
> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
>
>  This applies on top of v17 for origin/sb/submodule-parallel-update.
>
>  In case there are other reasons for origin/sb/submodule-parallel-update
>  to need a reroll I'll squash it in. But as this is a pure performance
>  optimization in a case we are not running into with that series and that
>  series is clashing with Davids refs backend series, I figure we may not
>  want to have a reroll for this fix alone.
>
>  Thanks,
>  Stefan
>
>
>  strbuf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/strbuf.c b/strbuf.c
> index 71345cd..5f6da82 100644
> --- a/strbuf.c
> +++ b/strbuf.c
> @@ -397,7 +397,7 @@ ssize_t strbuf_read_once(struct strbuf *sb, int fd, size_t hint)
>
>  ssize_t strbuf_write(struct strbuf *sb, FILE *f)
>  {
> -       return fwrite(sb->buf, 1, sb->len, f);
> +       return sb->len ? fwrite(sb->buf, 1, sb->len, f) : 0;
>  }
>
>
> --
> 2.7.2.374.ga5f0819.dirty
>
> --
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-- 
Duy