On 6/15/22 16:35, John Garry wrote:
On 15/06/2022 00:43, Damien Le Moal wrote:
On 6/15/22 03:20, Bart Van Assche wrote:
On 6/13/22 00:01, Damien Le Moal wrote:
On 6/9/22 19:29, John Garry wrote:
+ /*
+ * This determines how many commands the HBA will set aside
+ * for internal commands. This number will be added to
+ * @can_queue to calcumate the maximum number of simultaneous
s/calcumate/calculate
But this is weird. For SATA, can_queue is 32. Having reserved commands,
that number needs to stay the same. We cannot have more than 32 tags.
I think keeping can_queue as the max queue depth with at most
nr_reserved_cmds tags reserved is better.
+ * commands sent to the host.
+ */
+ int nr_reserved_cmds;
+1 for Damien's request. I also prefer to keep can_queue as the maximum
queue depth, whether or not nr_reserved_cmds has been set.
For non SATA drives, I still think that is a good idea. However, for
SATA,
we always have the internal tag command that is special. With John's
change, it would have to be reserved but that means we are down to 31 max
QD,
My intention is to keep regular tag depth at 32 for SATA. We add an
extra tag as a reserved tag. Indeed, this is called a 'tag', but it's
just really the placeholder for what will be the ATA_TAG_INTERNAL request.
About how we set scsi_host.can_queue, in this series we set .can_queue
as max regular tags, and the handling is as follows:
scsi_mq_setup_tags():
tag_set->queue_depth = shost->can_queue + shost->nr_reserved_cmds
tag_set->reserved_tags = shost->nr_reserved_cmds
So we honour the rule that blk_mq_tag_set.queue_depth is the total tag
depth, including reserved.
Incidentally I think Christoph prefers to keep .can_queue at total max
tags including reserved:
https://lore.kernel.org/linux-scsi/337339b7-6f4a-a25c-f11c-7f701b42d6a8@xxxxxxx/
so going backward several years... That internal tag for ATA does not
need to be reserved since this command is always used when the drive is
idle and no other NCQ commands are on-going.
So do you mean that ATA_TAG_INTERNAL qc is used for other commands apart
from internal commands?
No. It is used only for internal commands. What I meant to say is that
currently, internal commands are issued only on device scan, device
revalidate and error handling. All of these phases are done with the
device under EH with the issuing path stopped and all commands
completed, so no regular commands can be issued. Only internal ones, non
NCQ, using the ATA_TAG_INTERNAL. So strictly speaking, we should not
need to reserve that internal tag at all.
So the solution to all this is a likely a little more complicated if we
want to keep ATA max QD to 32.
thanks,
John
--
Damien Le Moal
Western Digital Research
