[Qemu-devel] [PATCH] Optimize screendump

[Avi Kivity <avi@redhat.com>]

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 <avi@redhat.com>
---
 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;
-- 
1.7.5.3