On 04/04/2017 05:32 PM, Omar Sandoval wrote:
On Tue, Apr 04, 2017 at 02:07:43PM +0200, Hannes Reinecke wrote:
Hi all,
as discussed recently most existing HBAs have a host-wide tagset which
does not map easily onto the per-queue tagset model of block mq.
This patchset implements a flag BLK_MQ_F_GLOBAL_TAGS for block-mq, which
enables the use of a shared tagset for all hardware queues.
The second patch adds a flag 'host_tagset' to the SCSI host template,
which allows drivers to enable the use of the global tagset.
This patchset probably has some performance implications as
there is a quite high probability of cache-bouncing when allocating
tags. Also I'm not quite sure if the implemented tagset sharing
is the correct way to handle things.
So this can be considered an RFC.
As usual, comments and reviews are welcome.
Hi, Hannes,
blk-mq already supports a shared tagset, and scsi-mq already uses that.
When we initialize a request queue, we add it to a tagset with
blk_mq_add_queue_set(), where we automatically mark the tagset as shared
if there is more than one queue using it. What does this do that
BLK_MQ_F_TAG_SHARED doesn't cover?
This is orthogonal to the BLK_MQ_F_TAG_SHARED flag.
That flag is covering the case for several block devices sharing the
same tagset.
My new flag is covering the case where several _hardware_ queues are
sharing the same tagset.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
