scsi: virtio_scsi: limit number of hw queues by nr_cpu_ids
commit 1978f30a87
upstream.
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.
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -891,6 +891,7 @@ static int virtscsi_probe(struct virtio_device *vdev)
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/* We need to know how many queues before we allocate. */
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num_queues = virtscsi_config_get(vdev, num_queues) ? : 1;
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num_queues = min_t(unsigned int, nr_cpu_ids, num_queues);
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num_targets = virtscsi_config_get(vdev, max_target) + 1;
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