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?
