On 2018年03月28日 12:01, haibinzhang(张海斌) wrote:
On 2018年03月27日 19:26, Jason wrote
On 2018年03月27日 17:12, haibinzhang wrote:
handle_tx() will delay rx for a long time when busy tx polling udp packets
with short length(ie: 1byte udp payload), because setting VHOST_NET_WEIGHT
takes into account only sent-bytes but no time.
Interesting.
Looking at vhost_can_busy_poll() it tries to poke pending vhost work and
exit the busy loop if it found one. So I believe something block the
work queuing. E.g did reverting 8241a1e466cd56e6c10472cac9c1ad4e54bc65db
fix the issue?
"busy tx polling" means using netperf send udp packets with 1 bytes payload(total 47bytes frame lenght),
and handle_tx() will be busy sending packets continuously.
It's not fair for handle_rx(),
so needs to limit max time of tx polling.
---
drivers/vhost/net.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 8139bc70ad7d..dc9218a3a75b 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -473,6 +473,7 @@ static void handle_tx(struct vhost_net *net)
struct socket *sock;
struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
bool zcopy, zcopy_used;
+ unsigned long start = jiffies;
Checking jiffies is tricky, need to convert it to ms or whatever others.
mutex_lock(&vq->mutex);
sock = vq->private_data;
@@ -580,7 +581,7 @@ static void handle_tx(struct vhost_net *net)
else
vhost_zerocopy_signal_used(net, vq);
vhost_net_tx_packet(net);
- if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
+ if (unlikely(total_len >= VHOST_NET_WEIGHT) || unlikely(jiffies - start >= 1)) {
How value 1 is determined here? And we need a complete test to make sure
this won't affect other use cases.
We just want <1ms ping latency, but actually we are not sure what value is reasonable.
We have some test results using netperf before this patch as follow,
Udp payload 1byte 100bytes 1000bytes 1400bytes
Ping avg latency 25ms 10ms 2ms 1.5ms
What is other testcases?
Something like https://patchwork.kernel.org/patch/10151645/.
Btw, you need use time_before() to properly handle jiffies overflow and
I would also suggest you to try something like #packets limit (e.g 64).
For long term, we definitely need more worker threads.
Thanks
Another thought is introduce another limit of #packets, but this need
benchmark too.
Thanks
vhost_poll_queue(&vq->poll);
break;
}
