Messages in this thread Patch in this message | | | From | "Richard W.M. Jones" <> | Subject | [PATCH 2/2] virtio: virtio_scsi: Set can_queue to the length of the virtqueue. | Date | Thu, 10 Aug 2017 17:40:35 +0100 |
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Since switching to blk-mq as the default in commit 5c279bd9e406 ("scsi: default to scsi-mq"), virtio-scsi LUNs consume about 10x as much kernel memory.
qemu currently allocates a fixed 128 entry virtqueue. can_queue currently is set to 1024. But with indirect descriptors, each command in the queue takes 1 virtqueue entry, so the number of commands which can be queued is equal to the length of the virtqueue.
Note I intend to send a patch to qemu to allow the virtqueue size to be configured from the qemu command line.
Thanks Paolo Bonzini, Christoph Hellwig.
Signed-off-by: Richard W.M. Jones <rjones@redhat.com> --- drivers/scsi/virtio_scsi.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c index 9be211d68b15..d6b4ff634c0d 100644 --- a/drivers/scsi/virtio_scsi.c +++ b/drivers/scsi/virtio_scsi.c @@ -972,6 +972,8 @@ static int virtscsi_probe(struct virtio_device *vdev) if (err) goto virtscsi_init_failed; + shost->can_queue = virtqueue_get_vring_size(vscsi->req_vqs[0].vq); + cmd_per_lun = virtscsi_config_get(vdev, cmd_per_lun) ?: 1; shost->cmd_per_lun = min_t(u32, cmd_per_lun, shost->can_queue); shost->max_sectors = virtscsi_config_get(vdev, max_sectors) ?: 0xFFFF; -- 2.13.1
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