[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] virtio-scsi: Add virtqueue_size parameter allow
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-scsi: Add virtqueue_size parameter allowing virtqueue size to be set. |
Date: |
Fri, 11 Aug 2017 11:40:32 +0100 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
On Thu, Aug 10, 2017 at 05:52:55PM +0100, Richard W.M. Jones wrote:
> Since Linux switched to blk-mq as the default in Linux commit
> 5c279bd9e406 ("scsi: default to scsi-mq"), virtio-scsi LUNs consume
> about 10x as much guest kernel memory.
>
> This commit allows you to choose the virtqueue size for each
> virtio-scsi-pci controller like this:
>
> -device virtio-scsi-pci,id=scsi,virtqueue_size=16
>
> The default is still 128 as before. Using smaller virtqueue_size
> allows many more disks to be added to small memory virtual machines.
> For a 1 vCPU, 500 MB, no swap VM I observed:
>
> With scsi-mq enabled (upstream kernel): 175 disks
> -"- ditto -"- virtqueue_size=64: 318 disks
> -"- ditto -"- virtqueue_size=16: 775 disks
> With scsi-mq disabled (kernel before 5c279bd9e406): 1755 disks
>
> Note that to have any effect, this requires a kernel patch:
>
> https://lkml.org/lkml/2017/8/10/689
>
> Signed-off-by: Richard W.M. Jones <address@hidden>
> ---
> hw/scsi/virtio-scsi.c | 8 +++++---
> include/hw/virtio/virtio-scsi.h | 2 +-
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index eb639442d1..aca1909a59 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -867,10 +867,10 @@ void virtio_scsi_common_realize(DeviceState *dev,
> s->sense_size = VIRTIO_SCSI_SENSE_DEFAULT_SIZE;
> s->cdb_size = VIRTIO_SCSI_CDB_DEFAULT_SIZE;
>
> - s->ctrl_vq = virtio_add_queue(vdev, VIRTIO_SCSI_VQ_SIZE, ctrl);
> - s->event_vq = virtio_add_queue(vdev, VIRTIO_SCSI_VQ_SIZE, evt);
> + s->ctrl_vq = virtio_add_queue(vdev, s->conf.virtqueue_size, ctrl);
> + s->event_vq = virtio_add_queue(vdev, s->conf.virtqueue_size, evt);
> for (i = 0; i < s->conf.num_queues; i++) {
> - s->cmd_vqs[i] = virtio_add_queue(vdev, VIRTIO_SCSI_VQ_SIZE, cmd);
> + s->cmd_vqs[i] = virtio_add_queue(vdev, s->conf.virtqueue_size, cmd);
> }
> }
Reviewed-by: Stefan Hajnoczi <address@hidden>
signature.asc
Description: PGP signature