Jason Wang
2018-Nov-23 03:00 UTC
[PATCH net-next 0/3] basic in order support for vhost_net
Hi: This series implement basic in order feature support for vhost_net. This feature requires both driver and device to use descriptors in order which can simplify the implementation and optimizaton for both side. The series also implement a simple optimization that avoid read available ring. Test shows 10% performance improvement. More optimizations could be done on top. Jason Wang (3): virtio: introduce in order feature bit vhost_net: support in order feature vhost: don't touch avail ring if in_order is negotiated drivers/vhost/net.c | 6 ++++-- drivers/vhost/vhost.c | 19 ++++++++++++------- include/uapi/linux/virtio_config.h | 6 ++++++ 3 files changed, 22 insertions(+), 9 deletions(-) -- 2.17.1
Jason Wang
2018-Nov-23 03:00 UTC
[PATCH net-next 1/3] virtio: introduce in order feature bit
Signed-off-by: Jason Wang <jasowang at redhat.com> --- include/uapi/linux/virtio_config.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h index 449132c76b1c..64496afc016d 100644 --- a/include/uapi/linux/virtio_config.h +++ b/include/uapi/linux/virtio_config.h @@ -75,6 +75,12 @@ */ #define VIRTIO_F_IOMMU_PLATFORM 33 +/* + * Device uses buffers in the same order in which they have been + * available. + */ +#define VIRTIO_F_IN_ORDER 35 + /* * Does the device support Single Root I/O Virtualization? */ -- 2.17.1
This makes vhost_net to support in order feature. This is as simple as
use datacopy path when it was negotiated. An alternative is not to
advertise in order when zerocopy is enabled which tends to be
suboptimal consider zerocopy may suffer from e.g HOL issues.
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
drivers/vhost/net.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index d919284f103b..bdf5de5a7eb2 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -74,7 +74,8 @@ enum {
VHOST_NET_FEATURES = VHOST_FEATURES |
(1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
(1ULL << VIRTIO_NET_F_MRG_RXBUF) |
- (1ULL << VIRTIO_F_IOMMU_PLATFORM)
+ (1ULL << VIRTIO_F_IOMMU_PLATFORM) |
+ (1ULL << VIRTIO_F_IN_ORDER)
};
enum {
@@ -971,7 +972,8 @@ static void handle_tx(struct vhost_net *net)
vhost_disable_notify(&net->dev, vq);
vhost_net_disable_vq(net, vq);
- if (vhost_sock_zcopy(sock))
+ if (vhost_sock_zcopy(sock) &&
+ !vhost_has_feature(vq, VIRTIO_F_IN_ORDER))
handle_tx_zerocopy(net, sock);
else
handle_tx_copy(net, sock);
--
2.17.1
Jason Wang
2018-Nov-23 03:00 UTC
[PATCH net-next 3/3] vhost: don't touch avail ring if in_order is negotiated
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 at 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
Michael S. Tsirkin
2018-Nov-23 15:41 UTC
[PATCH net-next 3/3] vhost: don't touch avail ring if in_order is negotiated
On Fri, Nov 23, 2018 at 11:00:16AM +0800, Jason Wang wrote:> 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.Well this isn't what the in order feature says in the spec. It forces the used ring to be in the same order as the available ring. So I don't think you can skip checking the available ring. And in fact depending on ring size and workload, using all of descriptor buffer might cause a slowdown. Rather you should be able to get about the same speedup, but from skipping checking the used ring in virtio.> 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 at 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
Michael S. Tsirkin
2018-Nov-23 15:49 UTC
[PATCH net-next 2/3] vhost_net: support in order feature
On Fri, Nov 23, 2018 at 11:00:15AM +0800, Jason Wang wrote:> This makes vhost_net to support in order feature. This is as simple as > use datacopy path when it was negotiated. An alternative is not to > advertise in order when zerocopy is enabled which tends to be > suboptimal consider zerocopy may suffer from e.g HOL issues.Well IIRC vhost_zerocopy_signal_used is used to actually reorder used ring to match available ring. So with a big comment explaining why it is so, we could just enable IN_ORDER there too.> > Signed-off-by: Jason Wang <jasowang at redhat.com> > --- > drivers/vhost/net.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index d919284f103b..bdf5de5a7eb2 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -74,7 +74,8 @@ enum { > VHOST_NET_FEATURES = VHOST_FEATURES | > (1ULL << VHOST_NET_F_VIRTIO_NET_HDR) | > (1ULL << VIRTIO_NET_F_MRG_RXBUF) | > - (1ULL << VIRTIO_F_IOMMU_PLATFORM) > + (1ULL << VIRTIO_F_IOMMU_PLATFORM) | > + (1ULL << VIRTIO_F_IN_ORDER) > }; > > enum { > @@ -971,7 +972,8 @@ static void handle_tx(struct vhost_net *net) > vhost_disable_notify(&net->dev, vq); > vhost_net_disable_vq(net, vq); > > - if (vhost_sock_zcopy(sock)) > + if (vhost_sock_zcopy(sock) && > + !vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) > handle_tx_zerocopy(net, sock); > else > handle_tx_copy(net, sock); > -- > 2.17.1