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[PATCH v2] virtio-blk: seg_max do not subtract 2 if host has VIRTIO_RING
From: |
zhaoxin\RockCuioc |
Subject: |
[PATCH v2] virtio-blk: seg_max do not subtract 2 if host has VIRTIO_RING_F_INDIRECT_DESC feature |
Date: |
Fri, 20 Nov 2020 13:03:03 +0800 |
v1 -> v2:
fix codestyle checked by checkpatch.pl
This patch modify virtio-blk seg_max when host has VIRTIO_RING_F_INDIRECT_DESC
feature, when read/write virtio-blk disk in direct mode,
this patch can make the bio reach 512k but not 504k if the user buffer physical
segments are all discontinuous,when use ceph the size of 504k
will affect performance.This patch should be used in guest kernel
version>=4.14, kernel after this version virtio driver does not judge
total_sg and vring num if the host supports indirect descriptor tables.
Signed-off-by: zhaoxin\RockCuioc <RockCui-oc@zhaoxin.com>
---
hw/block/virtio-blk.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index bac2d6f..40bbbd7 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -932,7 +932,11 @@ static void virtio_blk_update_config(VirtIODevice *vdev,
uint8_t *config)
blk_get_geometry(s->blk, &capacity);
memset(&blkcfg, 0, sizeof(blkcfg));
virtio_stq_p(vdev, &blkcfg.capacity, capacity);
- virtio_stl_p(vdev, &blkcfg.seg_max,
+ if virtio_host_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC)
+ virtio_stl_p(vdev, &blkcfg.seg_max,
+ s->conf.seg_max_adjust ? s->conf.queue_size : 128);
+ else
+ virtio_stl_p(vdev, &blkcfg.seg_max,
s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2);
virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls);
virtio_stl_p(vdev, &blkcfg.blk_size, blk_size);
--
2.10.1.windows.1
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