On Fri, Mar 11, 2016 at 05:34:52PM +0100, Christoph Hellwig wrote:
> Replace the while loop that unecessarily checks for a NULL bio in the fast
> path witch a simple goto loop.
s/witch/with/ ?
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> block/bio.c | 35 +++++++++++++++++------------------
> 1 file changed, 17 insertions(+), 18 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 67e51ac..e4682ec 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1745,26 +1745,25 @@ static inline bool bio_remaining_done(struct bio *bio)
> **/
> void bio_endio(struct bio *bio)
> {
> - while (bio) {
> - if (unlikely(!bio_remaining_done(bio)))
> - break;
> +again:
> + if (unlikely(!bio_remaining_done(bio)))
> + return;
>
> - /*
> - * Need to have a real endio function for chained bios,
> - * otherwise various corner cases will break (like stacking
> - * block devices that save/restore bi_end_io) - however, we want
> - * to avoid unbounded recursion and blowing the stack. Tail call
> - * optimization would handle this, but compiling with frame
> - * pointers also disables gcc's sibling call optimization.
> - */
> - if (bio->bi_end_io == bio_chain_endio) {
> - bio = __bio_chain_endio(bio);
> - } else {
> - if (bio->bi_end_io)
> - bio->bi_end_io(bio);
> - bio = NULL;
> - }
> + /*
> + * Need to have a real endio function for chained bios, otherwise
> + * various corner cases will break (like stacking block devices that
> + * save/restore bi_end_io) - however, we want to avoid unbounded
> + * recursion and blowing the stack. Tail call optimization would
> + * handle this, but compiling with frame pointers also disables
> + * gcc's sibling call optimization.
> + */
> + if (bio->bi_end_io == bio_chain_endio) {
> + bio = __bio_chain_endio(bio);
> + goto again;
> }
> +
> + if (bio->bi_end_io)
> + bio->bi_end_io(bio);
> }
> EXPORT_SYMBOL(bio_endio);
>
> --
> 2.1.4
>
> --
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Just out of curiosity, do you have any numbers for this change?
--
Johannes Thumshirn Storage
jthumshirn@xxxxxxx +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
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