From 765d704db1f583630d52dc14c1ea573db6783459 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Wed, 4 Jan 2017 09:33:23 -0800 Subject: [PATCH] raid5: only dispatch IO from raid5d for harddisk raid We made raid5 stripe handling multi-thread before. It works well for SSD. But for harddisk, the multi-threading creates more disk seek, so not always improve performance. For several hard disks based raid5, multi-threading is required as raid5d becames a bottleneck especially for sequential write. To overcome the disk seek issue, we only dispatch IO from raid5d if the array is harddisk based. Other threads can still handle stripes, but can't dispatch IO. Idealy, we should control IO dispatching order according to IO position interrnally. Right now we still depend on block layer, which isn't very efficient sometimes though. My setup has 9 harddisks, each disk can do around 180M/s sequential write. So in theory, the raid5 can do 180 * 8 = 1440M/s sequential write. The test machine uses an ATOM CPU. I measure sequential write with large iodepth bandwidth to raid array: without patch: ~600M/s without patch and group_thread_cnt=4: 750M/s with patch and group_thread_cnt=4: 950M/s with patch, group_thread_cnt=4, skip_copy=1: 1150M/s We are pretty close to the maximum bandwidth in the large iodepth iodepth case. The performance gap of small iodepth sequential write between software raid and theory value is still very big though, because we don't have an efficient pipeline. Cc: NeilBrown Cc: Song Liu Signed-off-by: Shaohua Li --- drivers/md/raid5.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++-- drivers/md/raid5.h | 4 ++++ 2 files changed, 57 insertions(+), 2 deletions(-) diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 3c7e106..9d744a8 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -863,6 +863,43 @@ static int use_new_offset(struct r5conf *conf, struct stripe_head *sh) return 1; } +static void flush_deferred_bios(struct r5conf *conf) +{ + struct bio_list tmp; + struct bio *bio; + + if (!conf->batch_bio_dispatch || !conf->group_cnt) + return; + + bio_list_init(&tmp); + spin_lock(&conf->pending_bios_lock); + bio_list_merge(&tmp, &conf->pending_bios); + bio_list_init(&conf->pending_bios); + spin_unlock(&conf->pending_bios_lock); + + while ((bio = bio_list_pop(&tmp))) + generic_make_request(bio); +} + +static void defer_bio_issue(struct r5conf *conf, struct bio *bio) +{ + /* + * change group_cnt will drain all bios, so this is safe + * + * A read generally means a read-modify-write, which usually means a + * randwrite, so we don't delay it + */ + if (!conf->batch_bio_dispatch || !conf->group_cnt || + bio_op(bio) == REQ_OP_READ) { + generic_make_request(bio); + return; + } + spin_lock(&conf->pending_bios_lock); + bio_list_add(&conf->pending_bios, bio); + spin_unlock(&conf->pending_bios_lock); + md_wakeup_thread(conf->mddev->thread); +} + static void raid5_end_read_request(struct bio *bi); static void @@ -1043,7 +1080,7 @@ again: trace_block_bio_remap(bdev_get_queue(bi->bi_bdev), bi, disk_devt(conf->mddev->gendisk), sh->dev[i].sector); - generic_make_request(bi); + defer_bio_issue(conf, bi); } if (rrdev) { if (s->syncing || s->expanding || s->expanded @@ -1088,7 +1125,7 @@ again: trace_block_bio_remap(bdev_get_queue(rbi->bi_bdev), rbi, disk_devt(conf->mddev->gendisk), sh->dev[i].sector); - generic_make_request(rbi); + defer_bio_issue(conf, rbi); } if (!rdev && !rrdev) { if (op_is_write(op)) @@ -6126,6 +6163,8 @@ static void raid5d(struct md_thread *thread) mutex_unlock(&conf->cache_size_mutex); } + flush_deferred_bios(conf); + r5l_flush_stripe_to_raid(conf->log); async_tx_issue_pending_all(); @@ -6711,6 +6750,18 @@ static struct r5conf *setup_conf(struct mddev *mddev) atomic_set(&conf->active_stripes, 0); atomic_set(&conf->preread_active_stripes, 0); atomic_set(&conf->active_aligned_reads, 0); + bio_list_init(&conf->pending_bios); + spin_lock_init(&conf->pending_bios_lock); + conf->batch_bio_dispatch = true; + rdev_for_each(rdev, mddev) { + if (test_bit(Journal, &rdev->flags)) + continue; + if (blk_queue_nonrot(bdev_get_queue(rdev->bdev))) { + conf->batch_bio_dispatch = false; + break; + } + } + conf->bypass_threshold = BYPASS_THRESHOLD; conf->recovery_disabled = mddev->recovery_disabled - 1; diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h index 1440fa2..ebb89bd 100644 --- a/drivers/md/raid5.h +++ b/drivers/md/raid5.h @@ -684,6 +684,10 @@ struct r5conf { int group_cnt; int worker_cnt_per_group; struct r5l_log *log; + + struct bio_list pending_bios; + spinlock_t pending_bios_lock; + bool batch_bio_dispatch; }; -- 2.7.4