dm-kcopyd: Delayed unplug of the queues This patch improves performance aby about 20% when writing to the snapshot origin. We keep track of two block devices to unplug (one for read and the other for write) and unplug them when exiting "do_work" thread. If there are more devices used (in theory it could happen, in practice it is rare), we unplug immediatelly. Signed-off-by: Mikulas Patocka --- drivers/md/dm-kcopyd.c | 35 ++++++++++++++++++++++++++++++++--- 1 file changed, 32 insertions(+), 3 deletions(-) Index: linux-2.6.34-fast/drivers/md/dm-kcopyd.c =================================================================== --- linux-2.6.34-fast.orig/drivers/md/dm-kcopyd.c 2010-07-22 16:08:36.000000000 +0200 +++ linux-2.6.34-fast/drivers/md/dm-kcopyd.c 2010-07-22 16:40:19.000000000 +0200 @@ -37,6 +37,8 @@ struct dm_kcopyd_client { unsigned int nr_pages; unsigned int nr_free_pages; + struct block_device *unplug[2]; + struct dm_io_client *io_client; wait_queue_head_t destroyq; @@ -308,6 +310,23 @@ static int run_complete_job(struct kcopy return 0; } +static void unplug(struct dm_kcopyd_client *kc, int queue) +{ + if (kc->unplug[queue] != NULL) { + blk_unplug(bdev_get_queue(kc->unplug[queue])); + kc->unplug[queue] = NULL; + } +} + +static void prepare_unplug(struct dm_kcopyd_client *kc, int queue, + struct block_device *bdev) +{ + if (likely(kc->unplug[queue] == bdev)) + return; + unplug(kc, queue); + kc->unplug[queue] = bdev; +} + static void complete_io(unsigned long error, void *context) { struct kcopyd_job *job = (struct kcopyd_job *) context; @@ -345,7 +364,7 @@ static int run_io_job(struct kcopyd_job { int r; struct dm_io_request io_req = { - .bi_rw = job->rw | (1 << BIO_RW_UNPLUG), + .bi_rw = job->rw, .mem.type = DM_IO_PAGE_LIST, .mem.ptr.pl = job->pages, .mem.offset = job->offset, @@ -354,10 +373,16 @@ static int run_io_job(struct kcopyd_job .client = job->kc->io_client, }; - if (job->rw == READ) + if (job->rw == READ) { r = dm_io(&io_req, 1, &job->source, NULL); - else + prepare_unplug(job->kc, READ, job->source.bdev); + } else { + if (unlikely(job->num_dests > 1)) + io_req.bi_rw |= 1 << BIO_RW_UNPLUG; r = dm_io(&io_req, job->num_dests, job->dests, NULL); + if (likely(!(io_req.bi_rw & (1 << BIO_RW_UNPLUG)))) + prepare_unplug(job->kc, WRITE, job->dests[0].bdev); + } return r; } @@ -439,6 +464,8 @@ static void do_work(struct work_struct * process_jobs(&kc->complete_jobs, kc, run_complete_job); process_jobs(&kc->pages_jobs, kc, run_pages_job); process_jobs(&kc->io_jobs, kc, run_io_job); + unplug(kc, READ); + unplug(kc, WRITE); } /* @@ -619,6 +646,8 @@ int dm_kcopyd_client_create(unsigned int INIT_LIST_HEAD(&kc->io_jobs); INIT_LIST_HEAD(&kc->pages_jobs); + memset(kc->unplug, 0, sizeof kc->unplug); + kc->job_pool = mempool_create_slab_pool(MIN_JOBS, _job_cache); if (!kc->job_pool) goto bad_slab;