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Re: [PATCH v1 2/4] virtio: increase virtuqueue size for virtio-scsi and
From: |
Stefan Hajnoczi |
Subject: |
Re: [PATCH v1 2/4] virtio: increase virtuqueue size for virtio-scsi and virtio-blk |
Date: |
Thu, 30 Jan 2020 14:58:40 +0000 |
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>
> ---
> 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"},
vhost-blk-device?! Who has this? It's not in qemu.git so please omit
this line. ;-)
On the other hand, do you want to do this for the vhost-user-blk,
vhost-user-scsi, and vhost-scsi devices that exist in qemu.git? Those
devices would benefit from better performance too.
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