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scsi: core: Avoid calling synchronize_rcu() for each device in scsi_host_block()

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scsi_host_block() calls scsi_internal_device_block() for each scsi_device and
scsi_internal_device_block() calls blk_mq_quiesce_queue() for each LUN.

Since synchronize_rcu() is called from blk_mq_quiesce_queue(), this can cause
substantial slowdowns on systems with many LUNs.

Use scsi_internal_device_block_nowait() to implement scsi_host_block() so it
is sufficient to run synchronize_rcu() once. This is safe since SCSI does not
set the BLK_MQ_F_BLOCKING flag.

[mkp: commit desc and comment tweaks]

Link: https://lore.kernel.org/r/20200423020713.332743-1-ming.lei@redhat.com
Cc: Steffen Maier <maier@linux.ibm.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Ming Lei 2020-04-23 10:07:13 +08:00 committed by Martin K. Petersen
parent 3fa65812c2
commit f983622ae6
1 changed files with 17 additions and 1 deletions
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18
drivers/scsi/scsi_lib.c
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@ -2841,11 +2841,27 @@ scsi_host_block(struct Scsi_Host *shost)
struct scsi_device *sdev;
int ret = 0;
/*
* Call scsi_internal_device_block_nowait so we can avoid
* calling synchronize_rcu() for each LUN.
*/
shost_for_each_device(sdev, shost) {
ret = scsi_internal_device_block(sdev);
mutex_lock(&sdev->state_mutex);
ret = scsi_internal_device_block_nowait(sdev);
mutex_unlock(&sdev->state_mutex);
if (ret)
break;
}
/*
* SCSI never enables blk-mq's BLK_MQ_F_BLOCKING flag so
* calling synchronize_rcu() once is enough.
*/
WARN_ON_ONCE(shost->tag_set.flags & BLK_MQ_F_BLOCKING);
if (!ret)
synchronize_rcu();
return ret;
}
EXPORT_SYMBOL_GPL(scsi_host_block);