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virtio: increase virtqueue size for virtio-scsi and virtio-blk

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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>
Message-id: 20200214074648.958-1-dplotnikov@virtuozzo.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Denis Plotnikov 2020-02-14 10:46:48 +03:00 • committed by Stefan Hajnoczi
parent 9ac5df20f5
commit c9b7d9ec21
3 changed files with 4 additions and 2 deletions
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2
hw/core/machine.c
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@ -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"},