src/patches/suse-2.6.27.25/patches.arch/ppc-spufs-07-Don-t-spu_acquire_saved-unnecessarily.patch

   1 Subject: Don't spu_acquire_saved unnecessarily in regs read
   2 From: Jeremy Kerr <jk@ozlabs.org>
   3 References: 447133 - LTC50070
   4
   5 With most file readers (eg cat, dd), reading a context's regs file will
   6 result in two reads: the first to read the data, and the second to
   7 return EOF. Because each read performs a spu_acquire_saved, we end up
   8 descheduling and re-scheduling the context twice.
   9
  10 This change does a simple check to see if we'd return EOF before
  11 calling spu_acquire_saved(), saving the extra schedule operation.
  12
  13 Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
  14 Signed-off-by: Olaf Hering <olh@suse.de>
  15 ---
  16  arch/powerpc/platforms/cell/spufs/file.c |    5 +++++
  17  1 file changed, 5 insertions(+)
  18
  19 --- a/arch/powerpc/platforms/cell/spufs/file.c
  20 +++ b/arch/powerpc/platforms/cell/spufs/file.c
  21 @@ -551,6 +551,11 @@ spufs_regs_read(struct file *file, char
  22         int ret;
  23         struct spu_context *ctx = file->private_data;
  24
  25 +       /* pre-check for file position: if we'd return EOF, there's no point
  26 +        * causing a deschedule */
  27 +       if (*pos >= sizeof(ctx->csa.lscsa->gprs))
  28 +               return 0;
  29 +
  30         ret = spu_acquire_saved(ctx);
  31         if (ret)
  32                 return ret;