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

[Denis Plotnikov]

On 30.01.2020 16:40, Michael S. Tsirkin wrote:
> 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.
Ok
Denis
> > ---
> >   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