Re: [PATCH 2/2] scsi: virtio_scsi: limit number of hw queues by nr_cpu_ids

[Stefan Hajnoczi]

On Wed, Mar 27, 2019 at 06:36:35PM +0800, 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 used by virtio-scsi, as it
> has (tag_set->nr_maps == 1), it 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-scsi would not be able to allocate
> more than maxcpus vectors in order to have a vector for each queue. As a
> result, it falls back into MSI-X with one vector for config and one shared
> for queues.
> 
> Considering above reasons, this patch limits the number of hw queues used
> by virtio-scsi by nr_cpu_ids.
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
> ---
>  drivers/scsi/virtio_scsi.c | 1 +
>  1 file changed, 1 insertion(+)

Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>

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