Commit f027faa2 authored Oct 16, 2008 by Jeremy Kerr

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>

parent 14f693ee

arch/powerpc/platforms/cell/spufs/file.c

+5 −0

Original line number	Original line	Diff line number	Diff line
	@@ -548,6 +548,11 @@ spufs_regs_read(struct file file, char __user buffer,
	int ret;		int ret;
	struct spu_context *ctx = file->private_data;		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);		ret = spu_acquire_saved(ctx);
	if (ret)		if (ret)
	return ret;		return ret;