On Thu, Feb 20, 2020 at 08:14:11AM -0800, Bart Van Assche wrote:
> On 2/20/20 2:05 AM, Ming Lei wrote:
> > On Wed, Feb 19, 2020 at 06:44:35PM -0800, Bart Van Assche wrote:
> > > blk_mq_map_queues() and multiple .map_queues() implementations expect that
> > > set->map[HCTX_TYPE_DEFAULT].nr_queues is set to the number of hardware
> >
> > Only single queue mapping expects set->map[HCTX_TYPE_DEFAULT].nr_queues
> > to be set->nr_hw_queues. For multiple mapping, set->nr_hw_queues should
> > be sum of each mapping's nr_queue.
>
> That's how it should work but that doesn't match what I found in the kernel
> tree. Here is an example of a .map_queues() implementation that depends on
> .nr_queues being set before it is called:
>
> static int scsi_map_queues(struct blk_mq_tag_set *set)
> {
> struct Scsi_Host *shost = container_of(set, struct Scsi_Host,
> tag_set);
>
> if (shost->hostt->map_queues)
> return shost->hostt->map_queues(shost);
> return blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
> }
>
> If shost->hostt->map_queues == NULL, the above function only works correctly
> if .nr_queues is set before this function is called. Additionally,
> scsi_map_queues() may call e.g. the following function:
>
> static int qla2xxx_map_queues(struct Scsi_Host *shost)
> {
> int rc;
> scsi_qla_host_t *vha = (scsi_qla_host_t *)shost->hostdata;
> struct blk_mq_queue_map *qmap =
> &shost->tag_set.map[HCTX_TYPE_DEFAULT];
>
> if (USER_CTRL_IRQ(vha->hw) || !vha->hw->mqiobase)
> rc = blk_mq_map_queues(qmap);
> else
> rc = blk_mq_pci_map_queues(qmap, vha->hw->pdev,
> vha->irq_offset);
> return rc;
> }
>
> Both blk_mq_map_queues() and blk_mq_pci_map_queues() assume that
> blk_mq_queue_map.nr_queues is set before these functions are called.
Actually, I suggested to do the following way:
if (set->nr_maps == 1)
set->map[HCTX_TYPE_DEFAULT].nr_queues = set->nr_hw_queues;
then people won't be confused wrt. relation between set->nr_hw_queues
and .nr_queues of each mapping.
Thanks,
Ming
