Re: [PATCH V4 11/12] scsi: make sure sdev->queue_depth is <= max(shost->can_queue, 1024)

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On 11/16/20 10:07 AM, Ming Lei wrote:
Limit scsi device's queue depth is less than max(host->can_queue, 1024)
in scsi_change_queue_depth(), and 1024 is big enough for saturating
current fast SCSI LUN(SSD, or raid volume on multiple SSDs).

We need this patch for replacing sdev->device_busy with sbitmap which
has to be pre-allocated with reasonable max depth.

Cc: Omar Sandoval <osandov@xxxxxx>
Cc: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx>
Cc: Sumanesh Samanta <sumanesh.samanta@xxxxxxxxxxxx>
Cc: Ewan D. Milne <emilne@xxxxxxxxxx>
Tested-by: Sumanesh Samanta <sumanesh.samanta@xxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
  drivers/scsi/scsi.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 24619c3bebd5..a28d48c850cf 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -214,6 +214,15 @@ void scsi_finish_command(struct scsi_cmnd *cmd)
  	scsi_io_completion(cmd, good_bytes);
  }
+
+/*
+ * 1024 is big enough for saturating the fast scsi LUN now
+ */
+static int scsi_device_max_queue_depth(struct scsi_device *sdev)
+{
+	return max_t(int, sdev->host->can_queue, 1024);
+}
+

Shouldn't this rather be initialized with scsi_host->can_queue?
These 'should be enough' settings inevitable turn out to be not enough in the long run ...

  /**
   * scsi_change_queue_depth - change a device's queue depth
   * @sdev: SCSI Device in question
@@ -223,6 +232,8 @@ void scsi_finish_command(struct scsi_cmnd *cmd)
   */
  int scsi_change_queue_depth(struct scsi_device *sdev, int depth)
  {
+	depth = min_t(int, depth, scsi_device_max_queue_depth(sdev));
+
  	if (depth > 0) {
  		sdev->queue_depth = depth;
  		wmb();


Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@xxxxxxx                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer



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