On 14/04/2021 18:03, Douglas Gilbert wrote:
On 2021-04-14 9:59 a.m., Kashyap Desai wrote:
I tried both - 5.12.0-rc1 and 5.11.0-rc2+ and there is a same
behavior.
Let me also check megaraid_sas and see if anything generic or this is
a special case of scsi_debug.
As I mentioned, it could be one generic issue wrt. SCHED_RESTART.
shared tags might have to restart all hctx since all share same tags.
Ming - I tried many combination on MR shared host tag driver but there is
no single instance of IO hang.
I will keep trying, but when I look at scsi_debug driver code I found
below odd settings in scsi_debug driver.
can_queue of adapter is set to 128 but queue_depth of sdev is set to 255.
If I apply below patch, scsi_debug driver's hang is also resolved.
Ideally
sdev->queue depth cannot exceed shost->can_queue.
Not sure why cmd_per_lun is 255 in scsi_debug driver which can easily
exceed can_queue. I will simulate something similar in MR driver and see
how it behaves w.r.t IO hang issue.
diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 70165be10f00..dded762540ee 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -218,7 +218,7 @@ static const char *sdebug_version_date = "20200710";
*/
#define SDEBUG_CANQUEUE_WORDS 3 /* a WORD is bits in a long */
#define SDEBUG_CANQUEUE (SDEBUG_CANQUEUE_WORDS * BITS_PER_LONG)
So SDEBUG_CANQUEUE is 3*64 = 192 and is a hard limit (it is used to
dimension an array). Should it be upped to 4, say? [That will slow things
down a bit if that is an issue.]
sdev_store_queue_depth() enforces that the sdev queue depth cannot
exceed can_queue.
I don't know why this is not also enforced in scsi_alloc_sdev(), or even
when registering the shost (for cmd_per_lun)
-#define DEF_CMD_PER_LUN 255
+#define DEF_CMD_PER_LUN SDEBUG_CANQUEUE
/* UA - Unit Attention; SA - Service Action; SSU - Start Stop Unit */
#define F_D_IN 1 /* Data-in command (e.g.
READ) */
@@ -7558,6 +7558,7 @@ static int sdebug_driver_probe(struct device *dev)
sdbg_host = to_sdebug_host(dev);
sdebug_driver_template.can_queue = sdebug_max_queue;
+ sdebug_driver_template.cmd_per_lun = sdebug_max_queue;
I'll push out a patch shortly.
Doug Gilbert
if (!sdebug_clustering)
sdebug_driver_template.dma_boundary = PAGE_SIZE - 1;
Thanks,
Ming
.
