Re: [PATCH v1 2/4] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Michael S. Tsirkin]

On Wed, Jan 29, 2020 at 05:07:00PM +0300, Denis Plotnikov wrote:
> 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 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 <address@hidden>
> Signed-off-by: Denis Plotnikov <address@hidden>


looks good but let's just patch each device separately.

> ---
>  hw/core/machine.c          | 3 +++
>  include/hw/virtio/virtio.h | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 3e288bfceb..8bc401d8b7 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -28,6 +28,9 @@
>  #include "hw/mem/nvdimm.h"
>  
>  GlobalProperty hw_compat_4_2[] = {
> +    { "virtio-blk-device", "queue-size", "128"},
> +    { "virtio-scsi-device", "virtqueue_size", "128"},
> +    { "vhost-blk-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/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index a66ea2368b..16d540e390 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -48,7 +48,7 @@ size_t virtio_feature_get_config_size(VirtIOFeature 
> *features,
>  typedef struct VirtQueue VirtQueue;
>  
>  #define VIRTQUEUE_MAX_SIZE 1024
> -#define VIRTQUEUE_DEFAULT_SIZE 128
> +#define VIRTQUEUE_DEFAULT_SIZE 256
>  
>  typedef struct VirtQueueElement
>  {
> -- 
> 2.17.0