On Tue, Jan 28, 2014 at 05:14:46PM +0800, Qin Chuanyu wrote: > On 2014/1/28 16:34, Michael S. Tsirkin wrote: > >On Tue, Jan 28, 2014 at 04:14:12PM +0800, Qin Chuanyu wrote: > >>according perf test result，I found that there are 5%-8% cpu cost on > >>softirq by use netif_rx_ni called in tun_get_user. > >> > >>so I changed the function which cause skb transmitted more quickly. > >>from > >> tun_get_user -> > >> netif_rx_ni(skb); > >>to > >> tun_get_user -> > >> rcu_read_lock_bh(); > >> netif_receive_skb(skb); > >> rcu_read_unlock_bh(); > >> > >>The test result is as below: > >> CPU: Intel(R) Xeon(R) CPU E5620 @ 2.40GHz > >> NIC: intel 82599 > >> Host OS/Guest OS:suse11sp3 > >> Qemu-1.6 > >> netperf udp 512(VM tx) > >> test model: VM->host->host > >> > >> modified before : 2.00Gbps 461146pps > >> modified after : 2.16Gbps 498782pps > >> > >>8% performance gained from this change, > >>Is there any problem for this patch ? > > > >I think it's okay - IIUC this way we are processing xmit directly > >instead of going through softirq. > >Was meaning to try this - I'm glad you are looking into this. > > > >Could you please check latency results? > > > netperf UDP_RR 512 > test model: VM->host->host > > modified before : 11108 > modified after : 11480 > > 3% gained by this patch > > Nice. What about CPU utilization? It's trivially easy to speed up networking by burning up a lot of CPU so we must make sure it's not doing that. And I think we should see some tests with TCP as well, and try several message sizes. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
