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Date: Wed, 11 Mar 2015 23:56:41 -0400
From: Mike Snitzer <snitzer@...hat.com>
To: Jens Axboe <axboe@...nel.dk>, Keith Busch <keith.busch@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
dm-devel@...hat.com
Subject: [PATCH 6/7] dm: optimize dm_mq_queue_rq to _not_ use kthread if using pure blk-mq
dm_mq_queue_rq() is in atomic context so care must be taken to not
sleep -- as such GFP_ATOMIC is used for the md->bs bioset allocations
and dm-mpath's call to blk_get_request(). In the future the bioset
allocations will hopefully go away (by removing support for partial
completions of a request).
But the kthread will still be used to queue work if blk-mq is used ontop
of old-style request_fn device(s). Also prepare for supporting DM
blk-mq ontop of old-style request_fn device(s) if a new dm-mod
'use_blk_mq' parameter is set.
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
---
drivers/md/dm.c | 65 +++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 45 insertions(+), 20 deletions(-)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b5409ac..b0c965a 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1074,9 +1074,10 @@ static void free_rq_clone(struct request *clone)
blk_rq_unprep_clone(clone);
- if (clone->q && clone->q->mq_ops)
+ if (clone->q->mq_ops)
tio->ti->type->release_clone_rq(clone);
- else
+ else if (!md->queue->mq_ops)
+ /* request_fn queue stacked on request_fn queue(s) */
free_clone_request(md, clone);
if (!md->queue->mq_ops)
@@ -1835,15 +1836,25 @@ static int setup_clone(struct request *clone, struct request *rq,
static struct request *clone_rq(struct request *rq, struct mapped_device *md,
struct dm_rq_target_io *tio, gfp_t gfp_mask)
{
- struct request *clone = alloc_clone_request(md, gfp_mask);
+ /*
+ * Do not allocate a clone if tio->clone was already set
+ * (see: dm_mq_queue_rq).
+ */
+ bool alloc_clone = !tio->clone;
+ struct request *clone;
- if (!clone)
- return NULL;
+ if (alloc_clone) {
+ clone = alloc_clone_request(md, gfp_mask);
+ if (!clone)
+ return NULL;
+ } else
+ clone = tio->clone;
blk_rq_init(NULL, clone);
if (setup_clone(clone, rq, tio, gfp_mask)) {
/* -ENOMEM */
- free_clone_request(md, clone);
+ if (alloc_clone)
+ free_clone_request(md, clone);
return NULL;
}
@@ -1861,7 +1872,8 @@ static void init_tio(struct dm_rq_target_io *tio, struct request *rq,
tio->orig = rq;
tio->error = 0;
memset(&tio->info, 0, sizeof(tio->info));
- init_kthread_work(&tio->work, map_tio_request);
+ if (md->kworker_task)
+ init_kthread_work(&tio->work, map_tio_request);
}
static struct dm_rq_target_io *prep_tio(struct request *rq,
@@ -1938,7 +1950,7 @@ static int map_request(struct dm_rq_target_io *tio, struct request *rq,
}
if (IS_ERR(clone))
return DM_MAPIO_REQUEUE;
- if (setup_clone(clone, rq, tio, GFP_NOIO)) {
+ if (setup_clone(clone, rq, tio, GFP_ATOMIC)) {
/* -ENOMEM */
ti->type->release_clone_rq(clone);
return DM_MAPIO_REQUEUE;
@@ -2403,7 +2415,7 @@ static void __bind_mempools(struct mapped_device *md, struct dm_table *t)
p->bs = NULL;
out:
- /* mempool bind completed, now no need any mempools in the table */
+ /* mempool bind completed, no longer need any mempools in the table */
dm_table_free_md_mempools(t);
}
@@ -2708,17 +2720,25 @@ static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
/* Init tio using md established in .init_request */
init_tio(tio, rq, md);
+ /*
+ * Establish tio->ti before queuing work (map_tio_request)
+ * or making direct call to map_request().
+ */
+ tio->ti = ti;
+
/* Clone the request if underlying devices aren't blk-mq */
if (dm_table_get_type(map) == DM_TYPE_REQUEST_BASED) {
- // FIXME: make the memory for clone part of the pdu
+ /* clone request is allocated at the end of the pdu */
+ tio->clone = (void *)blk_mq_rq_to_pdu(rq) + sizeof(struct dm_rq_target_io);
if (!clone_rq(rq, md, tio, GFP_ATOMIC))
return BLK_MQ_RQ_QUEUE_BUSY;
+ queue_kthread_work(&md->kworker, &tio->work);
+ } else {
+ /* Direct call is fine since .queue_rq allows allocations */
+ if (map_request(tio, rq, md) == DM_MAPIO_REQUEUE)
+ dm_requeue_unmapped_original_request(md, rq);
}
- /* Establish tio->ti before queuing work (map_tio_request) */
- tio->ti = ti;
- queue_kthread_work(&md->kworker, &tio->work);
-
return BLK_MQ_RQ_QUEUE_OK;
}
@@ -2731,6 +2751,7 @@ static struct blk_mq_ops dm_mq_ops = {
static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
{
+ unsigned md_type = dm_get_md_type(md);
struct request_queue *q;
int err;
@@ -2740,9 +2761,11 @@ static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
md->tag_set.numa_node = NUMA_NO_NODE;
md->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
md->tag_set.nr_hw_queues = 1;
- // FIXME: make the memory for non-blk-mq clone part of the pdu
- // would need to be done only if new 'use_blk_mq' is set in DM sysfs
- md->tag_set.cmd_size = sizeof(struct dm_rq_target_io);
+ if (md_type == DM_TYPE_REQUEST_BASED) {
+ /* make the memory for non-blk-mq clone part of the pdu */
+ md->tag_set.cmd_size = sizeof(struct dm_rq_target_io) + sizeof(struct request);
+ } else
+ md->tag_set.cmd_size = sizeof(struct dm_rq_target_io);
md->tag_set.driver_data = md;
err = blk_mq_alloc_tag_set(&md->tag_set);
@@ -2760,7 +2783,8 @@ static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
/* backfill 'mq' sysfs registration normally done in blk_register_queue */
blk_mq_register_disk(md->disk);
- init_rq_based_worker_thread(md);
+ if (md_type == DM_TYPE_REQUEST_BASED)
+ init_rq_based_worker_thread(md);
return 0;
@@ -2879,7 +2903,7 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
set_bit(DMF_FREEING, &md->flags);
spin_unlock(&_minor_lock);
- if (dm_request_based(md))
+ if (dm_request_based(md) && md->kworker_task)
flush_kthread_worker(&md->kworker);
/*
@@ -3133,7 +3157,8 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
*/
if (dm_request_based(md)) {
stop_queue(md->queue);
- flush_kthread_worker(&md->kworker);
+ if (md->kworker_task)
+ flush_kthread_worker(&md->kworker);
}
flush_workqueue(md->wq);
--
1.9.5 (Apple Git-50.3)
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