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 <d...@openvz.org> Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com> --- 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
