Re: [PATCHv2 8/10] xfs: avoid repeated pointer dereferences

Dave Chinner
2010-04-13T01:18:49Z

On Fri, Apr 09, 2010 at 05:30:42PM -0500, Alex Elder wrote:
> In xlog_find_cycle_start() use a local variable for some repeated
> operations rather than constantly updating the memory location
> whose address is passed in.

Won't the compiler optimise that out for us? i.e. does the dissassembly
of the function look any better before and after this change?

> Signed-off-by: Alex Elder <aelder@sgi.com>
>
> ---
> fs/xfs/xfs_log_recover.c | 83 ++++++++++++++++++++++++-----------------------
> fs/xfs/xfs_log_recover.c | 26 ++++++++++++++------------
> 1 file changed, 14 insertions(+), 12 deletions(-)
>
> Index: b/fs/xfs/xfs_log_recover.c
> ===================================================================
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -354,26 +354,28 @@ xlog_find_cycle_start(
> {
> xfs_caddr_t offset;
> xfs_daddr_t mid_blk;
> + xfs_daddr_t end_blk;
> uint mid_cycle;
> int error;
>
> - mid_blk = BLK_AVG(first_blk, *last_blk);
> - while (mid_blk != first_blk && mid_blk != *last_blk) {
> + ASSERT(last_blk != NULL);
> + end_blk = *last_blk;

FWIW, there is no need for that ASSERT there - the machine will
panic on the very next line, anyway....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com