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authorJeffle Xu <jefflexu@linux.alibaba.com>2019-11-18 04:50:38 +0300
committerMike Snitzer <snitzer@redhat.com>2019-11-18 18:03:12 +0300
commitd256d796279de0bdc227ff4daef565aa7e80c898 (patch)
treee26a7ba3db3faacf2515f0b26508c179b401525d /drivers/md
parentd537858ac8aaf4311b51240893add2fc62003b97 (diff)
downloadlinux-d256d796279de0bdc227ff4daef565aa7e80c898.tar.xz
dm thin: wakeup worker only when deferred bios exist
Single thread fio test (read, bs=4k, ioengine=libaio, iodepth=128, numjobs=1) over dm-thin device has poor performance versus bare nvme device. Further investigation with perf indicates that queue_work_on() consumes over 20% CPU time when doing IO over dm-thin device. The call stack is as follows. - 40.57% thin_map + 22.07% queue_work_on + 9.95% dm_thin_find_block + 2.80% cell_defer_no_holder 1.91% inc_all_io_entry.isra.33.part.34 + 1.78% bio_detain.isra.35 In cell_defer_no_holder(), wakeup_worker() is always called, no matter whether the tc->deferred_bio_list list is empty or not. In single thread IO model, this list is most likely empty. So skip waking up worker thread if tc->deferred_bio_list list is empty. Single thread IO performance improves from 448 MiB/s to 646 MiB/s (+44%) once the needless wake_worker() calls are properly skipped. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/dm-thin.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 85ada5ad2121..5a2c494cb552 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -882,12 +882,15 @@ static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *c
{
struct pool *pool = tc->pool;
unsigned long flags;
+ int has_work;
spin_lock_irqsave(&tc->lock, flags);
cell_release_no_holder(pool, cell, &tc->deferred_bio_list);
+ has_work = !bio_list_empty(&tc->deferred_bio_list);
spin_unlock_irqrestore(&tc->lock, flags);
- wake_worker(pool);
+ if (has_work)
+ wake_worker(pool);
}
static void thin_defer_bio(struct thin_c *tc, struct bio *bio);