From: Jason Wang <jasowang@redhat.com>
To: mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH net-next 3/3] vhost: don't touch avail ring if in_order is negotiated
Date: Fri, 23 Nov 2018 11:00:16 +0800 [thread overview]
Message-ID: <20181123030016.4924-4-jasowang@redhat.com> (raw)
In-Reply-To: <20181123030016.4924-1-jasowang@redhat.com>
Device use descriptors table in order, so there's no need to read
index from available ring. This eliminate the cache contention on
avail ring completely.
Virito-user + vhost_kernel + XDP_DROP gives about ~10% improvement on
TX from 4.8Mpps to 5.3Mpps on Intel(R) Core(TM) i7-5600U CPU @
2.60GHz.
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/vhost.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3a5f81a66d34..c8be151bc897 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2002,6 +2002,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
__virtio16 avail_idx;
__virtio16 ring_head;
int ret, access;
+ bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
/* Check it isn't doing very strange things with descriptor numbers. */
last_avail_idx = vq->last_avail_idx;
@@ -2034,15 +2035,19 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
/* Grab the next descriptor number they're advertising, and increment
* the index we've seen. */
- if (unlikely(vhost_get_avail(vq, ring_head,
- &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) {
- vq_err(vq, "Failed to read head: idx %d address %p\n",
- last_avail_idx,
- &vq->avail->ring[last_avail_idx % vq->num]);
- return -EFAULT;
+ if (!in_order) {
+ if (unlikely(vhost_get_avail(vq, ring_head,
+ &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) {
+ vq_err(vq, "Failed to read head: idx %d address %p\n",
+ last_avail_idx,
+ &vq->avail->ring[last_avail_idx % vq->num]);
+ return -EFAULT;
+ }
+ head = vhost16_to_cpu(vq, ring_head);
+ } else {
+ head = last_avail_idx & (vq->num - 1);
}
- head = vhost16_to_cpu(vq, ring_head);
/* If their number is silly, that's an error. */
if (unlikely(head >= vq->num)) {
--
2.17.1
next prev parent reply other threads:[~2018-11-23 3:00 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-23 3:00 [PATCH net-next 0/3] basic in order support for vhost_net Jason Wang
2018-11-23 3:00 ` [PATCH net-next 1/3] virtio: introduce in order feature bit Jason Wang
2018-11-23 3:00 ` [PATCH net-next 2/3] vhost_net: support in order feature Jason Wang
2018-11-23 15:49 ` Michael S. Tsirkin
2018-11-26 3:52 ` Jason Wang
2018-11-23 3:00 ` Jason Wang [this message]
2018-11-23 15:41 ` [PATCH net-next 3/3] vhost: don't touch avail ring if in_order is negotiated Michael S. Tsirkin
2018-11-26 4:01 ` Jason Wang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181123030016.4924-4-jasowang@redhat.com \
--to=jasowang@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mst@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=virtualization@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).