From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH] vhost-net: add time limitation for tx polling(Internet mail) Date: Wed, 28 Mar 2018 14:37:04 +0800 Message-ID: <0b1846d3-dfcf-df0c-f94c-65d414331d88@redhat.com> References: <88D661ADF6AFBF42B2AB88D8E7682B0901FC412A@EXMBX-SZMAIL011.tencent.com> Mime-Version: 1.0 Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit Cc: =?UTF-8?B?bGlkb25nY2hlbijpmYjnq4vkuJwp?= , =?UTF-8?B?eXVuZmFuZ3RhaSjlj7Dov5Dmlrkp?= To: =?UTF-8?B?aGFpYmluemhhbmco5byg5rW35paMKQ==?= , "mst@redhat.com" , "kvm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Return-path: In-Reply-To: <88D661ADF6AFBF42B2AB88D8E7682B0901FC412A@EXMBX-SZMAIL011.tencent.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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; >>> } >>