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Date: Thu, 21 Aug 2014 10:11:40 +0200 From: "Michael S. Tsirkin" <mst@...hat.com> To: Jason Wang <jasowang@...hat.com> Cc: davem@...emloft.net, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net-next 2/2] net: exit busy loop when another process is runnable On Thu, Aug 21, 2014 at 04:05:10PM +0800, Jason Wang wrote: > Rx busy loop does not scale well in the case when several parallel > sessions is active. This is because we keep looping even if there's > another process is runnable. For example, if that process is about to > send packet, keep busy polling in current process will brings extra > delay and damage the performance. > > This patch solves this issue by exiting the busy loop when there's > another process is runnable in current cpu. Simple test that pin two > netperf sessions in the same cpu in receiving side shows obvious > improvement: > > Before: > netperf -H 192.168.100.2 -T 0,0 -t TCP_RR -P 0 & \ > netperf -H 192.168.100.2 -T 1,0 -t TCP_RR -P 0 > 16384 87380 1 1 10.00 15513.74 > 16384 87380 > 16384 87380 1 1 10.00 15092.78 > 16384 87380 > > After: > netperf -H 192.168.100.2 -T 0,0 -t TCP_RR -P 0 & \ > netperf -H 192.168.100.2 -T 1,0 -t TCP_RR -P 0 > 16384 87380 1 1 10.00 23334.53 > 16384 87380 > 16384 87380 1 1 10.00 23327.58 > 16384 87380 > > Benchmark was done through two 8 cores Xeon machine back to back connected > with mlx4 through netperf TCP_RR test (busy_read were set to 50): > > sessions/bytes/before/after/+improvement%/busy_read=0/ > 1/1/30062.10/30034.72/+0%/20228.96/ > 16/1/214719.83/307669.01/+43%/268997.71/ > 32/1/231252.81/345845.16/+49%/336157.442/ > 64/512/212467.39/373464.93/+75%/397449.375/ > > Signed-off-by: Jason Wang <jasowang@...hat.com> > --- > include/net/busy_poll.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h > index 1d67fb6..8a33fb2 100644 > --- a/include/net/busy_poll.h > +++ b/include/net/busy_poll.h > @@ -109,7 +109,8 @@ static inline bool sk_busy_loop(struct sock *sk, int nonblock) > cpu_relax(); > > } while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) && > - !need_resched() && !busy_loop_timeout(end_time)); > + !need_resched() && !busy_loop_timeout(end_time) && > + nr_running_this_cpu() < 2); <= 1 would be a bit clearer? We want at most one process here. > > rc = !skb_queue_empty(&sk->sk_receive_queue); > out: > -- > 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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