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author | 2014-05-29 09:53:32 -0600 | |
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committer | 2014-05-29 09:53:32 -0600 | |
commit | 05f1dd5315217398fc8d122bdee80f96a9f21274 (patch) | |
tree | f1decfafa5f0d974d2f9c707a514bf68b9e2cddb /block/blk-merge.c | |
parent | block: remove 'magic' from struct blk_plug (diff) | |
download | linux-05f1dd5315217398fc8d122bdee80f96a9f21274.tar.gz linux-05f1dd5315217398fc8d122bdee80f96a9f21274.tar.bz2 linux-05f1dd5315217398fc8d122bdee80f96a9f21274.zip |
block: add queue flag for disabling SG merging
If devices are not SG starved, we waste a lot of time potentially
collapsing SG segments. Enough that 1.5% of the CPU time goes
to this, at only 400K IOPS. Add a queue flag, QUEUE_FLAG_NO_SG_MERGE,
which just returns the number of vectors in a bio instead of looping
over all segments and checking for collapsible ones.
Add a BLK_MQ_F_SG_MERGE flag so that drivers can opt-in on the sg
merging, if they so desire.
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-merge.c')
-rw-r--r-- | block/blk-merge.c | 28 |
1 files changed, 21 insertions, 7 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c index 6c583f9c5b65..b3bf0df0f4c2 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -13,7 +13,7 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q, struct bio *bio) { struct bio_vec bv, bvprv = { NULL }; - int cluster, high, highprv = 1; + int cluster, high, highprv = 1, no_sg_merge; unsigned int seg_size, nr_phys_segs; struct bio *fbio, *bbio; struct bvec_iter iter; @@ -35,12 +35,21 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q, cluster = blk_queue_cluster(q); seg_size = 0; nr_phys_segs = 0; + no_sg_merge = test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags); + high = 0; for_each_bio(bio) { bio_for_each_segment(bv, bio, iter) { /* + * If SG merging is disabled, each bio vector is + * a segment + */ + if (no_sg_merge) + goto new_segment; + + /* * the trick here is making sure that a high page is - * never considered part of another segment, since that - * might change with the bounce page. + * never considered part of another segment, since + * that might change with the bounce page. */ high = page_to_pfn(bv.bv_page) > queue_bounce_pfn(q); if (!high && !highprv && cluster) { @@ -84,11 +93,16 @@ void blk_recalc_rq_segments(struct request *rq) void blk_recount_segments(struct request_queue *q, struct bio *bio) { - struct bio *nxt = bio->bi_next; + if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags)) + bio->bi_phys_segments = bio->bi_vcnt; + else { + struct bio *nxt = bio->bi_next; + + bio->bi_next = NULL; + bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio); + bio->bi_next = nxt; + } - bio->bi_next = NULL; - bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio); - bio->bi_next = nxt; bio->bi_flags |= (1 << BIO_SEG_VALID); } EXPORT_SYMBOL(blk_recount_segments); |