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| author | Jens Axboe <axboe@fb.com> | 2014-05-29 09:53:32 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2014-05-29 09:53:32 -0600 |
| commit | 05f1dd5315217398fc8d122bdee80f96a9f21274 (patch) | |
| tree | f1decfafa5f0d974d2f9c707a514bf68b9e2cddb /block | |
| parent | 4d92a9beb39d80a7d8ff7c04ae12a10290105ae5 (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')
| -rw-r--r-- | block/blk-merge.c | 28 | ||||
| -rw-r--r-- | block/blk-mq.c | 3 |
2 files changed, 24 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); diff --git a/block/blk-mq.c b/block/blk-mq.c index f27fe44230c2..f98d977fd150 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1829,6 +1829,9 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set) q->mq_ops = set->ops; q->queue_flags |= QUEUE_FLAG_MQ_DEFAULT; + if (!(set->flags & BLK_MQ_F_SG_MERGE)) + q->queue_flags |= 1 << QUEUE_FLAG_NO_SG_MERGE; + q->sg_reserved_size = INT_MAX; INIT_WORK(&q->requeue_work, blk_mq_requeue_work); |