In [0], CPU usage for blk_mq_queue_tag_busy_iter() was optimized, but
there are still periodic call of blk_mq_queue_tag_busy_iter() from
below context. Below context is used for block layer timer to find out
potential expired command (per request queue) which requires tag iteration
almost every 5 seconds(defined BLK_MAX_TIMEOUT) for each request queue.
kthread
worker_thread
process_one_work
blk_mq_timeout_work
blk_mq_queue_tag_busy_iter
bt_iter
blk_mq_find_and_get_req
_raw_spin_lock_irqsave
native_queued_spin_lock_slowpath
Changes in this patch optimize extra iterations of tags in case of
shared_tags. One iteration of shared_tags can give expected results for
iterate function.
Setup - AMD64 Gen-4.0 Server.
64 Virtual Drive created using 16 Nvme drives + mpi3mr driver (in
shared_tags mode)
Test command -
fio 64.fio --rw=randread --bs=4K --iodepth=32 --numjobs=2 --ioscheduler=mq-deadline --disk_util=0
Without this patch on 5.16.0-rc5, mpi3mr driver in shared_tags mode can
give 4.0M IOPs vs expected to get ~6.0M.
Snippet of perf top
25.42% [kernel] [k] native_queued_spin_lock_slowpath
3.95% [kernel] [k] cpupri_set
2.05% [kernel] [k] __blk_mq_get_driver_tag
1.67% [kernel] [k] __rcu_read_unlock
1.63% [kernel] [k] check_preemption_disabled
After applying this patch on 5.16.0-rc5, mpi3mr driver in shared_tags
mode reach up to 5.8M IOPs.
Snippet of perf top
7.95% [kernel] [k] native_queued_spin_lock_slowpath
5.61% [kernel] [k] cpupri_set
2.98% [kernel] [k] acpi_processor_ffh_cstate_enter
2.49% [kernel] [k] read_tsc
2.15% [kernel] [k] check_preemption_disabled
[0] https://lore.kernel.org/all/9b092ca49e9b5415772cd950a3c12584@xxxxxxxxxxxxxx/
Cc: linux-block@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: john.garry@xxxxxxxxxx
Cc: ming.lei@xxxxxxxxxx
Cc: sathya.prakash@xxxxxxxxxxxx
Signed-off-by: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx>
---
block/blk-mq-tag.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 995336abee33..3e0a8e79f966 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -253,7 +253,8 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
if (!rq)
return true;
- if (rq->q == hctx->queue && rq->mq_hctx == hctx)
+ if (rq->q == hctx->queue && (rq->mq_hctx == hctx ||
+ blk_mq_is_shared_tags(hctx->flags)))
ret = iter_data->fn(hctx, rq, iter_data->data, reserved);
blk_mq_put_rq_ref(rq);
return ret;
@@ -484,6 +485,14 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
if (tags->nr_reserved_tags)
bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
+
+ /* In case of shared bitmap if shared_tags is allocated, it is not required
+ * to iterate all the hctx. Looping one hctx is good enough.
+ */
+ if (blk_mq_is_shared_tags(hctx->flags)) {
+ blk_queue_exit(q);
+ return;
+ }
}
blk_queue_exit(q);
}
--
2.18.1
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