Paolo Abeni
2018-Apr-24 08:34 UTC
[PATCH] vhost_net: use packet weight for rx handler, too
Similar to commit a2ac99905f1e ("vhost-net: set packet weight of
tx polling to 2 * vq size"), we need a packet-based limit for
handler_rx, too - elsewhere, under rx flood with small packets,
tx can be delayed for a very long time, even without busypolling.
The pkt limit applied to handle_rx must be the same applied by
handle_tx, or we will get unfair scheduling between rx and tx.
Tying such limit to the queue length makes it less effective for
large queue length values and can introduce large process
scheduler latencies, so a constant valued is used - likewise
the existing bytes limit.
The selected limit has been validated with PVP[1] performance
test with different queue sizes:
queue size 256 512 1024
baseline 366 354 362
weight 128 715 723 670
weight 256 740 745 733
weight 512 600 460 583
weight 1024 423 427 418
A packet weight of 256 gives peek performances in under all the
tested scenarios.
No measurable regression in unidirectional performance tests has
been detected.
[1]
https://developers.redhat.com/blog/2017/06/05/measuring-and-comparing-open-vswitch-performance/
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
---
drivers/vhost/net.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index bbf38befefb2..c4b49fca4871 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -46,8 +46,10 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy
TX;"
#define VHOST_NET_WEIGHT 0x80000
/* Max number of packets transferred before requeueing the job.
- * Using this limit prevents one virtqueue from starving rx. */
-#define VHOST_NET_PKT_WEIGHT(vq) ((vq)->num * 2)
+ * Using this limit prevents one virtqueue from starving others with small
+ * pkts.
+ */
+#define VHOST_NET_PKT_WEIGHT 256
/* MAX number of TX used buffers for outstanding zerocopy */
#define VHOST_MAX_PEND 128
@@ -587,7 +589,7 @@ static void handle_tx(struct vhost_net *net)
vhost_zerocopy_signal_used(net, vq);
vhost_net_tx_packet(net);
if (unlikely(total_len >= VHOST_NET_WEIGHT) ||
- unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT(vq))) {
+ unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT)) {
vhost_poll_queue(&vq->poll);
break;
}
@@ -769,6 +771,7 @@ static void handle_rx(struct vhost_net *net)
struct socket *sock;
struct iov_iter fixup;
__virtio16 num_buffers;
+ int recv_pkts = 0;
mutex_lock_nested(&vq->mutex, 0);
sock = vq->private_data;
@@ -872,7 +875,8 @@ static void handle_rx(struct vhost_net *net)
if (unlikely(vq_log))
vhost_log_write(vq, vq_log, log, vhost_len);
total_len += vhost_len;
- if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
+ if (unlikely(total_len >= VHOST_NET_WEIGHT) ||
+ unlikely(++recv_pkts >= VHOST_NET_PKT_WEIGHT)) {
vhost_poll_queue(&vq->poll);
goto out;
}
--
2.14.3
On 2018?04?24? 16:34, Paolo Abeni wrote:> Similar to commit a2ac99905f1e ("vhost-net: set packet weight of > tx polling to 2 * vq size"), we need a packet-based limit for > handler_rx, too - elsewhere, under rx flood with small packets, > tx can be delayed for a very long time, even without busypolling. > > The pkt limit applied to handle_rx must be the same applied by > handle_tx, or we will get unfair scheduling between rx and tx. > Tying such limit to the queue length makes it less effective for > large queue length values and can introduce large process > scheduler latencies, so a constant valued is used - likewise > the existing bytes limit. > > The selected limit has been validated with PVP[1] performance > test with different queue sizes: > > queue size 256 512 1024 > > baseline 366 354 362 > weight 128 715 723 670 > weight 256 740 745 733 > weight 512 600 460 583 > weight 1024 423 427 418 > > A packet weight of 256 gives peek performances in under all the > tested scenarios. > > No measurable regression in unidirectional performance tests has > been detected. > > [1] https://developers.redhat.com/blog/2017/06/05/measuring-and-comparing-open-vswitch-performance/ > > Signed-off-by: Paolo Abeni <pabeni at redhat.com> > --- > drivers/vhost/net.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index bbf38befefb2..c4b49fca4871 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -46,8 +46,10 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;" > #define VHOST_NET_WEIGHT 0x80000 > > /* Max number of packets transferred before requeueing the job. > - * Using this limit prevents one virtqueue from starving rx. */ > -#define VHOST_NET_PKT_WEIGHT(vq) ((vq)->num * 2) > + * Using this limit prevents one virtqueue from starving others with small > + * pkts. > + */ > +#define VHOST_NET_PKT_WEIGHT 256 > > /* MAX number of TX used buffers for outstanding zerocopy */ > #define VHOST_MAX_PEND 128 > @@ -587,7 +589,7 @@ static void handle_tx(struct vhost_net *net) > vhost_zerocopy_signal_used(net, vq); > vhost_net_tx_packet(net); > if (unlikely(total_len >= VHOST_NET_WEIGHT) || > - unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT(vq))) { > + unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT)) { > vhost_poll_queue(&vq->poll); > break; > } > @@ -769,6 +771,7 @@ static void handle_rx(struct vhost_net *net) > struct socket *sock; > struct iov_iter fixup; > __virtio16 num_buffers; > + int recv_pkts = 0; > > mutex_lock_nested(&vq->mutex, 0); > sock = vq->private_data; > @@ -872,7 +875,8 @@ static void handle_rx(struct vhost_net *net) > if (unlikely(vq_log)) > vhost_log_write(vq, vq_log, log, vhost_len); > total_len += vhost_len; > - if (unlikely(total_len >= VHOST_NET_WEIGHT)) { > + if (unlikely(total_len >= VHOST_NET_WEIGHT) || > + unlikely(++recv_pkts >= VHOST_NET_PKT_WEIGHT)) { > vhost_poll_queue(&vq->poll); > goto out; > }The numbers looks impressive. Acked-by: Jason Wang <jasowang at redhat.com> Thanks!
David Miller
2018-Apr-24 14:02 UTC
[PATCH] vhost_net: use packet weight for rx handler, too
From: Paolo Abeni <pabeni at redhat.com> Date: Tue, 24 Apr 2018 10:34:36 +0200> Similar to commit a2ac99905f1e ("vhost-net: set packet weight of > tx polling to 2 * vq size"), we need a packet-based limit for > handler_rx, too - elsewhere, under rx flood with small packets, > tx can be delayed for a very long time, even without busypolling. > > The pkt limit applied to handle_rx must be the same applied by > handle_tx, or we will get unfair scheduling between rx and tx. > Tying such limit to the queue length makes it less effective for > large queue length values and can introduce large process > scheduler latencies, so a constant valued is used - likewise > the existing bytes limit. > > The selected limit has been validated with PVP[1] performance > test with different queue sizes: > > queue size 256 512 1024 > > baseline 366 354 362 > weight 128 715 723 670 > weight 256 740 745 733 > weight 512 600 460 583 > weight 1024 423 427 418 > > A packet weight of 256 gives peek performances in under all the > tested scenarios. > > No measurable regression in unidirectional performance tests has > been detected. > > [1] https://developers.redhat.com/blog/2017/06/05/measuring-and-comparing-open-vswitch-performance/ > > Signed-off-by: Paolo Abeni <pabeni at redhat.com>Applied to net-next, thanks.
Apparently Analagous Threads
- [RFC PATCH net-next 02/12] vhost_net: introduce vhost_exceeds_weight()
- [RFC PATCH net-next 02/12] vhost_net: introduce vhost_exceeds_weight()
- [RFC PATCH net-next 03/12] vhost_net: introduce vhost_has_more_pkts()
- [PATCH net 0/4] Prevent vhost kthread from hogging CPU
- [PATCH] vhost-net: set packet weight of tx polling to 2 * vq size