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 <[email protected]> --- 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); rc = !skb_queue_empty(&sk->sk_receive_queue); out: -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
