Re: [dm-devel] dm-multipath test scripts

[Bart Van Assche <bart.vanassche@sandisk.com>]

On 02/20/16 01:42, Hannes Reinecke wrote:
> ATM the only SCSI driver to support SCSI-mq properly are lpfc, virtio, 
> and fnic. None of the other driver have been modified, and I suspect the 
> performance might be less than stellar.

Hello Hannes,

Before scsi-mq support was added to the above drivers it was added
to the ib_srp driver. Apparently today there are multiple drivers
that support multiple hardware queues:

$ git grep -nH 'nr_hw_queues = [^1]' | grep -vE 'block/blk-mq|scsi/scsi_lib'
drivers/block/null_blk.c:667:		nullb->tag_set.nr_hw_queues = submit_queues;
drivers/block/virtio_blk.c:638:	vblk->tag_set.nr_hw_queues = vblk->num_vqs;
drivers/block/xen-blkfront.c:927:	info->tag_set.nr_hw_queues = info->nr_rings;
drivers/infiniband/ulp/srp/ib_srp.c:3337:	target->scsi_host->nr_hw_queues = target->ch_count;
drivers/nvme/host/pci.c:1680:		dev->tagset.nr_hw_queues = dev->online_queues - 1;
drivers/scsi/lpfc/lpfc_init.c:3318:	shost->nr_hw_queues = phba->cfg_fcp_io_channel;
drivers/scsi/virtio_scsi.c:1008:	shost->nr_hw_queues = num_queues;

Performance data is available in http://events.linuxfoundation.org/sites/events/files/slides/Vault%20-%20scsi-mq%20v2.pdf.

Bart.