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| author | Ming Lei <ming.lei@redhat.com> | 2020-04-23 10:07:13 +0800 |
|---|---|---|
| committer | Martin K. Petersen <martin.petersen@oracle.com> | 2020-04-24 18:21:15 -0400 |
| commit | f983622ae60516d634008c7b1ff9ffff4f7bb8ae (patch) | |
| tree | 11f5a5aa347e1ebec3429d67f33665c3b4283ced /drivers/scsi/scsi_lib.c | |
| parent | 3fa65812c20297bf71724c6138c0aed8531012f9 (diff) | |
| download | linux-rt-f983622ae60516d634008c7b1ff9ffff4f7bb8ae.tar.gz | |
scsi: core: Avoid calling synchronize_rcu() for each device in scsi_host_block()
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>
Diffstat (limited to 'drivers/scsi/scsi_lib.c')
| -rw-r--r-- | drivers/scsi/scsi_lib.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 47835c4b4ee0..ff0449fbe3a0 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -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); |