Re: [PATCH v2] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Typo 'virtuqueue' in subject.

On 2/13/20 3:59 PM, Denis Plotnikov wrote:
> v1:
>    * seg_max default value changing removed
> 

^^^ This part ...

> ---
> The goal is to reduce the amount of requests issued by a guest on
> 1M reads/writes. This rises the performance up to 4% on that kind of
> disk access pattern.
> 
> The maximum chunk size to be used for the guest disk accessing is
> limited with seg_max parameter, which represents the max amount of
> pices in the scatter-geather list in one guest disk request.
> 
> Since seg_max is virqueue_size dependent, increasing the virtqueue
> size increases seg_max, which, in turn, increases the maximum size
> of data to be read/write from a guest disk.
> 
> More details in the original problem statment:
> https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
> 
> Suggested-by: Denis V. Lunev <den@openvz.org>
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---

... goes here.

>   hw/block/virtio-blk.c | 2 +-
>   hw/core/machine.c     | 2 ++
>   hw/scsi/virtio-scsi.c | 2 +-
>   3 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 09f46ed85f..142863a3b2 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -1272,7 +1272,7 @@ static Property virtio_blk_properties[] = {
>       DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
>                       true),
>       DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
> -    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
> +    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 256),
>       DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
>       DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
>                        IOThread *),
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 2501b540ec..3427d6cf4c 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -28,6 +28,8 @@
>   #include "hw/mem/nvdimm.h"
>   
>   GlobalProperty hw_compat_4_2[] = {
> +    { "virtio-blk-device", "queue-size", "128"},
> +    { "virtio-scsi-device", "virtqueue_size", "128"},
>       { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
>       { "virtio-blk-device", "seg-max-adjust", "off"},
>       { "virtio-scsi-device", "seg_max_adjust", "off"},
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 3b61563609..472bbd233b 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -965,7 +965,7 @@ 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),
> +                                         parent_obj.conf.virtqueue_size, 256),
>       DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI,
>                         parent_obj.conf.seg_max_adjust, true),
>       DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors,
>