On Wed, Feb 03, 2010 at 03:45:11PM +0800, Shaohua Li wrote: > the endio is done at reverse order of bio vectors. That means for a sequential > read, the page first submitted will finish last in a bio. Considering we will > do checksum (making cache hot) for every page, this does introduce delay (and > chance to squeeze cache used soon) for pages submitted at the begining. I > don't observe obvious performance difference with below patch at my simple > test, > but seems more natural to finish read in the order they are submitted.
Interesting, I wonder if we'd be able to see this on a higher throughput system. Jens, care to give it a shot (patch below)? -chris Signed-off-by: Shaohua Li <[email protected]> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 96577e8..4df0c56 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -1750,7 +1750,8 @@ static void end_bio_extent_writepage(struct bio *bio, int err) static void end_bio_extent_readpage(struct bio *bio, int err) { int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); - struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1; + struct bio_vec *bvec_end = bio->bi_io_vec + bio->bi_vcnt - 1; + struct bio_vec *bvec = bio->bi_io_vec; struct extent_io_tree *tree; u64 start; u64 end; @@ -1773,7 +1774,7 @@ static void end_bio_extent_readpage(struct bio *bio, int err) else whole_page = 0; - if (--bvec >= bio->bi_io_vec) + if (++bvec <= bvec_end) prefetchw(&bvec->bv_page->flags); if (uptodate && tree->ops && tree->ops->readpage_end_io_hook) { @@ -1818,7 +1819,7 @@ static void end_bio_extent_readpage(struct bio *bio, int err) } check_page_locked(tree, page); } - } while (bvec >= bio->bi_io_vec); + } while (bvec <= bvec_end); bio_put(bio); } -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
