From: sagig@dev.mellanox.co.il (Sagi Grimberg)
Subject: dm-multipath low performance with blk-mq
Date: Mon, 18 Jan 2016 14:04:38 +0200 [thread overview]
Message-ID: <569CD4D6.2040908@dev.mellanox.co.il> (raw)
Hi All,
I've recently tried out dm-multipath over a "super-fast" nvme device
and noticed a serious lock contention in dm-multipath that requires some
extra attention. The nvme device is a simple loopback device emulation
backed by null_blk device.
With this I've seen dm-multipath pushing around ~470K IOPs while
the native (loopback) nvme performance can easily push up to 1500K+ IOPs.
perf output [1] reveals a huge lock contention on the multipath lock
which is a per-dm_target contention point which seem to defeat the
purpose of blk-mq i/O path.
The two current bottlenecks seem to come from multipath_busy and
__multipath_map. Would it make better sense to move to a percpu_ref
model with freeze/unfreeze logic for updates similar to what blk-mq
is doing?
Thoughts?
[1]:
- 23.67% fio [kernel.kallsyms] [k]
queued_spin_lock_slowpath
- queued_spin_lock_slowpath
- 51.40% _raw_spin_lock_irqsave
- 99.98% multipath_busy
dm_mq_queue_rq
__blk_mq_run_hw_queue
blk_mq_run_hw_queue
blk_mq_insert_requests
blk_mq_flush_plug_list
blk_flush_plug_list
blk_finish_plug
do_io_submit
SyS_io_submit
entry_SYSCALL_64_fastpath
+ io_submit
- 48.05% _raw_spin_lock_irq
- 100.00% __multipath_map
multipath_clone_and_map
target_message
dispatch_io
__blk_mq_run_hw_queue
blk_mq_run_hw_queue
blk_mq_insert_requests
blk_mq_flush_plug_list
blk_flush_plug_list
blk_finish_plug
do_io_submit
SyS_io_submit
entry_SYSCALL_64_fastpath
+ io_submit
+ 1.70% fio [kernel.kallsyms] [k] __blk_mq_run_hw_queue
+ 1.56% fio fio [.] get_io_u
+ 1.06% fio [kernel.kallsyms] [k] blk_account_io_start
+ 0.92% fio fio [.] do_io
+ 0.82% fio [kernel.kallsyms] [k] do_blockdev_direct_IO
+ 0.81% fio [kernel.kallsyms] [k]
blk_mq_hctx_mark_pending
+ 0.75% fio [kernel.kallsyms] [k] __blk_mq_alloc_request
+ 0.75% fio [kernel.kallsyms] [k] __bt_get
+ 0.69% fio [kernel.kallsyms] [k] do_direct_IO
next reply other threads:[~2016-01-18 12:04 UTC|newest]
Thread overview: 127+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-18 12:04 Sagi Grimberg [this message]
2016-01-19 10:37 ` dm-multipath low performance with blk-mq Sagi Grimberg
2016-01-19 22:45 ` Mike Snitzer
2016-01-19 22:45 ` Mike Snitzer
2016-01-25 21:40 ` Mike Snitzer
2016-01-25 21:40 ` Mike Snitzer
2016-01-25 23:37 ` [dm-devel] " Benjamin Marzinski
2016-01-25 23:37 ` Benjamin Marzinski
2016-01-26 13:29 ` Mike Snitzer
2016-01-26 13:29 ` Mike Snitzer
2016-01-26 14:01 ` Hannes Reinecke
2016-01-26 14:47 ` Mike Snitzer
2016-01-26 14:47 ` Mike Snitzer
2016-01-26 14:56 ` Christoph Hellwig
2016-01-26 14:56 ` Christoph Hellwig
2016-01-26 15:27 ` Mike Snitzer
2016-01-26 15:27 ` Mike Snitzer
2016-01-26 15:57 ` Benjamin Marzinski
2016-01-27 11:14 ` Sagi Grimberg
2016-01-27 11:14 ` Sagi Grimberg
2016-01-27 17:48 ` Mike Snitzer
2016-01-27 17:48 ` Mike Snitzer
2016-01-27 17:51 ` Jens Axboe
2016-01-27 17:51 ` Jens Axboe
2016-01-27 18:16 ` Mike Snitzer
2016-01-27 18:16 ` Mike Snitzer
2016-01-27 18:26 ` Jens Axboe
2016-01-27 18:26 ` Jens Axboe
2016-01-27 19:14 ` Mike Snitzer
2016-01-27 19:14 ` Mike Snitzer
2016-01-27 19:50 ` Jens Axboe
2016-01-27 19:50 ` Jens Axboe
2016-01-27 17:56 ` Sagi Grimberg
2016-01-27 17:56 ` Sagi Grimberg
2016-01-27 18:42 ` Mike Snitzer
2016-01-27 18:42 ` Mike Snitzer
2016-01-27 19:49 ` Jens Axboe
2016-01-27 19:49 ` Jens Axboe
2016-01-27 20:45 ` Mike Snitzer
2016-01-27 20:45 ` Mike Snitzer
2016-01-29 23:35 ` Mike Snitzer
2016-01-29 23:35 ` Mike Snitzer
2016-01-30 8:52 ` Hannes Reinecke
2016-01-30 8:52 ` Hannes Reinecke
2016-01-30 19:12 ` Mike Snitzer
2016-01-30 19:12 ` Mike Snitzer
2016-02-01 6:46 ` Hannes Reinecke
2016-02-01 6:46 ` Hannes Reinecke
2016-02-03 18:04 ` Mike Snitzer
2016-02-03 18:04 ` Mike Snitzer
2016-02-03 18:24 ` Mike Snitzer
2016-02-03 18:24 ` Mike Snitzer
2016-02-03 19:22 ` Mike Snitzer
2016-02-03 19:22 ` Mike Snitzer
2016-02-04 6:54 ` Hannes Reinecke
2016-02-04 6:54 ` Hannes Reinecke
2016-02-04 13:54 ` Mike Snitzer
2016-02-04 13:54 ` Mike Snitzer
2016-02-04 13:58 ` Hannes Reinecke
2016-02-04 13:58 ` Hannes Reinecke
2016-02-04 14:09 ` Mike Snitzer
2016-02-04 14:09 ` Mike Snitzer
2016-02-04 14:32 ` Hannes Reinecke
2016-02-04 14:32 ` Hannes Reinecke
2016-02-04 14:44 ` Mike Snitzer
2016-02-04 14:44 ` Mike Snitzer
2016-02-05 15:13 ` [RFC PATCH] dm: fix excessive dm-mq context switching Mike Snitzer
2016-02-05 15:13 ` Mike Snitzer
2016-02-05 18:05 ` Mike Snitzer
2016-02-05 18:05 ` Mike Snitzer
2016-02-05 19:19 ` Mike Snitzer
2016-02-05 19:19 ` Mike Snitzer
2016-02-07 15:41 ` Sagi Grimberg
2016-02-07 15:41 ` Sagi Grimberg
2016-02-07 16:07 ` Mike Snitzer
2016-02-07 16:07 ` Mike Snitzer
2016-02-07 16:42 ` Sagi Grimberg
2016-02-07 16:42 ` Sagi Grimberg
2016-02-07 16:37 ` Bart Van Assche
2016-02-07 16:37 ` Bart Van Assche
2016-02-07 16:43 ` Sagi Grimberg
2016-02-07 16:43 ` Sagi Grimberg
2016-02-07 16:53 ` Mike Snitzer
2016-02-07 16:53 ` Mike Snitzer
2016-02-07 16:54 ` Sagi Grimberg
2016-02-07 16:54 ` Sagi Grimberg
2016-02-07 17:20 ` Mike Snitzer
2016-02-07 17:20 ` Mike Snitzer
2016-02-08 12:21 ` Sagi Grimberg
2016-02-08 12:21 ` Sagi Grimberg
2016-02-08 14:34 ` Mike Snitzer
2016-02-08 14:34 ` Mike Snitzer
2016-02-09 7:50 ` Hannes Reinecke
2016-02-09 7:50 ` Hannes Reinecke
2016-02-09 14:55 ` Mike Snitzer
2016-02-09 14:55 ` Mike Snitzer
2016-02-09 15:32 ` Hannes Reinecke
2016-02-09 15:32 ` Hannes Reinecke
2016-02-10 0:45 ` Mike Snitzer
2016-02-10 0:45 ` Mike Snitzer
2016-02-11 1:50 ` RCU-ified dm-mpath for testing/review Mike Snitzer
2016-02-11 3:35 ` Mike Snitzer
2016-02-11 3:35 ` Mike Snitzer
2016-02-11 15:34 ` Mike Snitzer
2016-02-11 15:34 ` Mike Snitzer
2016-02-12 15:18 ` Hannes Reinecke
2016-02-12 15:18 ` Hannes Reinecke
2016-02-12 15:26 ` Mike Snitzer
2016-02-12 15:26 ` Mike Snitzer
2016-02-12 16:04 ` Hannes Reinecke
2016-02-12 16:04 ` Hannes Reinecke
2016-02-12 18:00 ` Mike Snitzer
2016-02-12 18:00 ` Mike Snitzer
2016-02-15 6:47 ` Hannes Reinecke
2016-02-15 6:47 ` Hannes Reinecke
2016-01-26 1:49 ` [dm-devel] dm-multipath low performance with blk-mq Benjamin Marzinski
2016-01-26 1:49 ` Benjamin Marzinski
2016-01-26 16:03 ` Mike Snitzer
2016-01-26 16:03 ` Mike Snitzer
2016-01-26 16:44 ` Christoph Hellwig
2016-01-26 16:44 ` Christoph Hellwig
2016-01-27 2:09 ` Mike Snitzer
2016-01-27 2:09 ` Mike Snitzer
2016-01-27 11:10 ` Sagi Grimberg
2016-01-27 11:10 ` Sagi Grimberg
2016-01-26 21:40 ` [dm-devel] " Benjamin Marzinski
2016-01-26 21:40 ` Benjamin Marzinski
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