Messages in this thread | | | Subject | Re: [PATCH] vhost-net: add time limitation for tx polling(Internet mail) | From | Jason Wang <> | Date | Thu, 29 Mar 2018 10:00:51 +0800 |
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On 2018年03月28日 23:31, Michael S. Tsirkin wrote: > On Wed, Mar 28, 2018 at 02:37:04PM +0800, Jason Wang wrote: >> >> 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). > Maybe a ring size?
Yes or a factor of ring size.
> >> For long term, we definitely need more worker threads. >> >> Thanks > Only helps when you have spare CPUs.
Right.
Thanks
>>>> Another thought is introduce another limit of #packets, but this need >>>> benchmark too. >>>> >>>> Thanks >>>> >>>>> vhost_poll_queue(&vq->poll); >>>>> break; >>>>> }
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