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Re: [Qemu-devel] [PATCH] virtio-scsi: Add virtqueue_size parameter allow
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-scsi: Add virtqueue_size parameter allowing virtqueue size to be set. |
Date: |
Fri, 11 Aug 2017 00:22:20 +0300 |
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>
Looks reasonable but pls remember to repost after the release.
> ---
> 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);
> }
> }
>
> @@ -917,6 +917,8 @@ static void virtio_scsi_device_unrealize(DeviceState
> *dev, Error **errp)
>
> static Property virtio_scsi_properties[] = {
> DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues,
> 1),
> + DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI,
> + parent_obj.conf.virtqueue_size,
> 128),
> DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI,
> parent_obj.conf.max_sectors,
> 0xFFFF),
> DEFINE_PROP_UINT32("cmd_per_lun", VirtIOSCSI,
> parent_obj.conf.cmd_per_lun,
> diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
> index de6ae5a9f6..4c0bcdb788 100644
> --- a/include/hw/virtio/virtio-scsi.h
> +++ b/include/hw/virtio/virtio-scsi.h
> @@ -32,7 +32,6 @@
> #define VIRTIO_SCSI(obj) \
> OBJECT_CHECK(VirtIOSCSI, (obj), TYPE_VIRTIO_SCSI)
>
> -#define VIRTIO_SCSI_VQ_SIZE 128
> #define VIRTIO_SCSI_MAX_CHANNEL 0
> #define VIRTIO_SCSI_MAX_TARGET 255
> #define VIRTIO_SCSI_MAX_LUN 16383
> @@ -48,6 +47,7 @@ typedef struct virtio_scsi_config VirtIOSCSIConfig;
>
> struct VirtIOSCSIConf {
> uint32_t num_queues;
> + uint32_t virtqueue_size;
> uint32_t max_sectors;
> uint32_t cmd_per_lun;
> #ifdef CONFIG_VHOST_SCSI
> --
> 2.13.1