* [PATCH] scsi: avoid to run synchronize_rcu for each device in scsi_host_block
@ 2020-04-22 10:14 Ming Lei
2020-04-22 15:06 ` Bart Van Assche
2020-04-22 16:19 ` Steffen Maier
0 siblings, 2 replies; 3+ messages in thread
From: Ming Lei @ 2020-04-22 10:14 UTC (permalink / raw)
To: James Bottomley, linux-scsi, Martin K . Petersen
Cc: Ming Lei, Bart Van Assche, Christoph Hellwig, Dexuan Cui,
Hannes Reinecke
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. However synchronize_rcu is
run from blk_mq_quiesce_queue().
This way may become unnecessary slow in case of lots of LUNs.
So use scsi_internal_device_block() to implement scsi_host_block(),
and just run once synchronize_rcu() because scsi never supports
tagset of BLK_MQ_F_BLOCKING.
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>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/scsi/scsi_lib.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 47835c4b4ee0..089ac92ac6c3 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2841,11 +2841,22 @@ scsi_host_block(struct Scsi_Host *shost)
struct scsi_device *sdev;
int ret = 0;
+ /*
+ * Call scsi_internal_device_block_nowait then we can avoid to
+ * run synchronize_rcu() one time for every 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;
}
+
+ WARN_ON_ONCE(shost->tag_set.flags & BLK_MQ_F_BLOCKING);
+
+ if (!ret)
+ synchronize_rcu();
return ret;
}
EXPORT_SYMBOL_GPL(scsi_host_block);
--
2.25.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] scsi: avoid to run synchronize_rcu for each device in scsi_host_block
2020-04-22 10:14 [PATCH] scsi: avoid to run synchronize_rcu for each device in scsi_host_block Ming Lei
@ 2020-04-22 15:06 ` Bart Van Assche
2020-04-22 16:19 ` Steffen Maier
1 sibling, 0 replies; 3+ messages in thread
From: Bart Van Assche @ 2020-04-22 15:06 UTC (permalink / raw)
To: Ming Lei, James Bottomley, linux-scsi, Martin K . Petersen
Cc: Christoph Hellwig, Dexuan Cui, Hannes Reinecke
On 4/22/20 3:14 AM, Ming Lei wrote:
> So use scsi_internal_device_block() to implement scsi_host_block(),
> and just run once synchronize_rcu() because scsi never supports
> tagset of BLK_MQ_F_BLOCKING.
Please add a reference to BLK_MQ_F_BLOCKING as a comment in the modified
code.
Thanks,
Bart.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] scsi: avoid to run synchronize_rcu for each device in scsi_host_block
2020-04-22 10:14 [PATCH] scsi: avoid to run synchronize_rcu for each device in scsi_host_block Ming Lei
2020-04-22 15:06 ` Bart Van Assche
@ 2020-04-22 16:19 ` Steffen Maier
1 sibling, 0 replies; 3+ messages in thread
From: Steffen Maier @ 2020-04-22 16:19 UTC (permalink / raw)
To: Ming Lei, James Bottomley, linux-scsi, Martin K . Petersen
Cc: Bart Van Assche, Christoph Hellwig, Dexuan Cui, Hannes Reinecke
On 4/22/20 12:14 PM, Ming Lei wrote:
> 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. However synchronize_rcu is
> run from blk_mq_quiesce_queue().
>
> This way may become unnecessary slow in case of lots of LUNs.
>
> So use scsi_internal_device_block() to implement scsi_host_block(),
scsi_internal_device_block()
=?=>
scsi_internal_device_block_nowait()
> and just run once synchronize_rcu() because scsi never supports
> tagset of BLK_MQ_F_BLOCKING.
>
> 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>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> drivers/scsi/scsi_lib.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 47835c4b4ee0..089ac92ac6c3 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -2841,11 +2841,22 @@ scsi_host_block(struct Scsi_Host *shost)
> struct scsi_device *sdev;
> int ret = 0;
>
> + /*
> + * Call scsi_internal_device_block_nowait then we can avoid to
> + * run synchronize_rcu() one time for every 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;
> }
> +
> + WARN_ON_ONCE(shost->tag_set.flags & BLK_MQ_F_BLOCKING);
> +
> + if (!ret)
> + synchronize_rcu();
> return ret;
> }
> EXPORT_SYMBOL_GPL(scsi_host_block);
>
--
Mit freundlichen Gruessen / Kind regards
Steffen Maier
Linux on IBM Z Development
https://www.ibm.com/privacy/us/en/
IBM Deutschland Research & Development GmbH
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-04-22 10:14 [PATCH] scsi: avoid to run synchronize_rcu for each device in scsi_host_block Ming Lei
2020-04-22 15:06 ` Bart Van Assche
2020-04-22 16:19 ` Steffen Maier
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