On 03/06/2019 08:46, Hannes Reinecke wrote:
On 6/3/19 9:37 AM, Ming Lei wrote:
On Mon, Jun 03, 2019 at 08:08:18AM +0200, Hannes Reinecke wrote:
On 6/1/19 1:06 AM, Ming Lei wrote:
On Fri, May 31, 2019 at 12:26:56PM +0200, Hannes Reinecke wrote:
On 5/31/19 10:46 AM, Ming Lei wrote:
[ .. ]
First we check for the 'slot_index_alloc()' callback to handle weird v2
allocation rules, _then_ we look for a tag, and only if we do _not_ have
a tag we're using the bitmap.
OK, looks I miss the above change.
And the bitmap is already correctly sized, as otherwise we'd have a
clash between internal and tagged I/O commands even now.
But now the big problem is in the following two line code:
+ else if (blk_tag != (u32)-1)
+ rc = blk_mq_unique_tag_to_tag(blk_tag);
Request from different blk-mq hw queue has same tag returned from
blk_mq_unique_tag_to_tag().
Yes, but the sbitmap allocator will ensure that each command will get a
unique tag.
Each hw queue has independent sbitmap allocator, so commands with same
tag can come from different hw queue.
It does not for SCSI.
See below.
So you meant this RFC patch depends on the host-wide tags patchset I
posted?
Now the biggest question is that if V3 hw supports per-queue tags,
If yes, it should be real MQ hardware, otherwise I guess commands with
same tag at the same time may not work for host-wide tags.
Of course you can't have different commands with the same tag. But the
sbitmap allocator prevents this from happening, as for host-wide tags
the tagset is _shared_ between all devices, so the sbitmap allocator
will only ever run on _one_ tagset for all commands.
But blk-mq doesn't support host-wide tags yet, so how can this single
patch work?
Wrong. It does:
struct request_queue *scsi_mq_alloc_queue(struct scsi_device *sdev)
{
sdev->request_queue = blk_mq_init_queue(&sdev->host->tag_set);
if (IS_ERR(sdev->request_queue))
return NULL;
sdev->request_queue->queuedata = sdev;
__scsi_init_queue(sdev->host, sdev->request_queue);
blk_queue_flag_set(QUEUE_FLAG_SCSI_PASSTHROUGH, sdev->request_queue);
return sdev->request_queue;
}
IE every scsi device is using the tagset from the host.
Hi Hannes,
Do you think that we have a problem for the bsg devices we create in
SCSI transport SAS, in that they don't seem to use the same host tagset?
I'm looking at scsi_transport_sas.c::sas_bsg_initialise()->bsg_setup_queue()
Thanks,
John
Cheers,
Hannes
