Re: [Qemu-devel] [PATCH] Optimize screendump

[malc]

On Sun, 19 Jun 2011, Avi Kivity wrote:

CONFORMING TO
       The     four     functions    getc_unlocked(), getchar_unlocked(),
       putc_unlocked(), putchar_unlocked() are in POSIX.1-2001.
       The non-standard *_unlocked() variants occur on a few Unix systems, and
       are available in recent glibc.  They should probably not be used.

> When running kvm-autotest, fputc() is often the second highest (sometimes #1)
> function showing up in a profile.  This is due to fputc() locking the file
> for every byte written.
> 
> Optimize by using fputc_unlocked().  Since the file is local to the caller,
> clearly no locking is needed.  According to the manual, _GNU_SOURCE is all
> that's needed for the function to be present.
> 
> Signed-off-by: Avi Kivity <address@hidden>
> ---
>  hw/vga.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/vga.c b/hw/vga.c
> index d5bc582..8b63358 100644
> --- a/hw/vga.c
> +++ b/hw/vga.c
> @@ -2369,9 +2369,9 @@ int ppm_save(const char *filename, struct 
> DisplaySurface *ds)
>                  (ds->pf.gmax + 1);
>              b = ((v >> ds->pf.bshift) & ds->pf.bmax) * 256 /
>                  (ds->pf.bmax + 1);
> -            fputc(r, f);
> -            fputc(g, f);
> -            fputc(b, f);
> +            fputc_unlocked(r, f);
> +            fputc_unlocked(g, f);
> +            fputc_unlocked(b, f);
>              d += ds->pf.bytes_per_pixel;
>          }
>          d1 += ds->linesize;
> 

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