powerpc/spufs: Don't spu_acquire_saved unnecessarily in regs read
With most file readers (eg cat, dd), reading a context's regs file will
result in two reads: the first to read the data, and the second to
return EOF. Because each read performs a spu_acquire_saved, we end up
descheduling and re-scheduling the context twice.
This change does a simple check to see if we'd return EOF before
calling spu_acquire_saved(), saving the extra schedule operation.
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/arch/powerpc/platforms/cell/spufs/file.c b/arch/powerpc/platforms/cell/spufs/file.c
index f139cd8..b6f7b91 100644
--- a/arch/powerpc/platforms/cell/spufs/file.c
+++ b/arch/powerpc/platforms/cell/spufs/file.c
@@ -548,6 +548,11 @@
int ret;
struct spu_context *ctx = file->private_data;
+ /* pre-check for file position: if we'd return EOF, there's no point
+ * causing a deschedule */
+ if (*pos >= sizeof(ctx->csa.lscsa->gprs))
+ return 0;
+
ret = spu_acquire_saved(ctx);
if (ret)
return ret;