What block driver controls the block device for which the performance
regression
has been observed? How many hardware queues were created by that block
driver
(see also /sys/block/*/mq/...)?
Just confirming that we have only 1 queue:
/sys/block/sdc/mq/0 as example
Hi Bart,
Here's the shost init for our SCSI LLDD:
http://elixir.free-electrons.com/linux/latest/source/drivers/scsi/hisi_sas/hisi_sas_main.c#L1736
So we don't set hr_hw_queues (which would mean = 0), so this should set
shost->tag_set.nr_hw_queues to 1 in scsi_mq_setup_tags().
FWIW, I can confirm sysfs entry when I get hw access tomorrow.
John
I'm asking this because the number of hardware
queues controls which I/O scheduler is selected as default. From
block/elevator.c:
if (q->mq_ops) {
if (q->nr_hw_queues == 1)
e = elevator_get("mq-deadline", false);
if (!e)
return 0;
} else
e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
Bart.
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