Re: [PATCH 0/2] Limit number of hw queues by nr_cpu_ids for virtio-blk and virtio-scsi

From: Jens Axboe
Date: Wed Apr 10 2019 - 10:18:58 EST

On 3/27/19 4:36 AM, Dongli Zhang wrote:
> When tag_set->nr_maps is 1, the block layer limits the number of hw queues
> by nr_cpu_ids. No matter how many hw queues are use by
> virtio-blk/virtio-scsi, as they both have (tag_set->nr_maps == 1), they
> can use at most nr_cpu_ids hw queues.
> In addition, specifically for pci scenario, when the 'num-queues' specified
> by qemu is more than maxcpus, virtio-blk/virtio-scsi would not be able to
> allocate more than maxcpus vectors in order to have a vector for each
> queue. As a result, they fall back into MSI-X with one vector for config
> and one shared for queues.
> Considering above reasons, this patch set limits the number of hw queues
> used by nr_cpu_ids for both virtio-blk and virtio-scsi.

I picked both up for 5.1.

Jens Axboe