From f983622ae60516d634008c7b1ff9ffff4f7bb8ae Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Thu, 23 Apr 2020 10:07:13 +0800 Subject: [PATCH] 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 Cc: Bart Van Assche Cc: Christoph Hellwig Cc: Dexuan Cui Cc: Hannes Reinecke Reviewed-by: Christoph Hellwig Reviewed-by: Hannes Reinecke Signed-off-by: Ming Lei Signed-off-by: Martin K. Petersen --- drivers/scsi/scsi_lib.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) 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);