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Date: Sun, 20 May 2012 20:13:58 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: Denys Fedoryshchenko <denys@...p.net.lb> Cc: netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net, jeffrey.t.kirsher@...el.com, jesse.brandeburg@...el.com, therbert@...gle.com, davem@...emloft.net Subject: Re: Strange latency spikes/TX network stalls on Sun Fire X4150(x86) and e1000e On Fri, 2012-05-18 at 17:04 +0300, Denys Fedoryshchenko wrote: > It seems logic in BQL has serious issues. The most bad thing, if > and it is empty. So in result, instead of eliminating latency, it is > adding it. There is maybe a misunderstanding here. BQL by itself only reduce amount of buffering in TX ring. Now there's still the Qdisc layer. On my laptop (e1000e NIC), and default pfifo_fast I can immediately see the difference in ping results if I launch a single netperf TCP_STREAM in another window : 1480 bytes from 172.30.42.1: icmp_seq=5047 ttl=64 time=0.185 ms 1480 bytes from 172.30.42.1: icmp_seq=5048 ttl=64 time=0.198 ms 1480 bytes from 172.30.42.1: icmp_seq=5049 ttl=64 time=0.255 ms 1480 bytes from 172.30.42.1: icmp_seq=5050 ttl=64 time=0.182 ms 1480 bytes from 172.30.42.1: icmp_seq=5051 ttl=64 time=0.182 ms 1480 bytes from 172.30.42.1: icmp_seq=5052 ttl=64 time=0.226 ms 1480 bytes from 172.30.42.1: icmp_seq=5053 ttl=64 time=0.186 ms 1480 bytes from 172.30.42.1: icmp_seq=5054 ttl=64 time=0.190 ms 1480 bytes from 172.30.42.1: icmp_seq=5055 ttl=64 time=0.223 ms 1480 bytes from 172.30.42.1: icmp_seq=5056 ttl=64 time=0.178 ms 1480 bytes from 172.30.42.1: icmp_seq=5057 ttl=64 time=0.191 ms 1480 bytes from 172.30.42.1: icmp_seq=5058 ttl=64 time=0.229 ms 1480 bytes from 172.30.42.1: icmp_seq=5059 ttl=64 time=0.229 ms 1480 bytes from 172.30.42.1: icmp_seq=5060 ttl=64 time=0.213 ms 1480 bytes from 172.30.42.1: icmp_seq=5061 ttl=64 time=0.187 ms 1480 bytes from 172.30.42.1: icmp_seq=5062 ttl=64 time=0.944 ms 1480 bytes from 172.30.42.1: icmp_seq=5063 ttl=64 time=4.67 ms 1480 bytes from 172.30.42.1: icmp_seq=5064 ttl=64 time=8.55 ms 1480 bytes from 172.30.42.1: icmp_seq=5065 ttl=64 time=12.8 ms 1480 bytes from 172.30.42.1: icmp_seq=5066 ttl=64 time=16.9 ms 1480 bytes from 172.30.42.1: icmp_seq=5067 ttl=64 time=20.5 ms 1480 bytes from 172.30.42.1: icmp_seq=5068 ttl=64 time=24.3 ms 1480 bytes from 172.30.42.1: icmp_seq=5069 ttl=64 time=27.0 ms 1480 bytes from 172.30.42.1: icmp_seq=5070 ttl=64 time=26.8 ms 1480 bytes from 172.30.42.1: icmp_seq=5071 ttl=64 time=26.7 ms 1480 bytes from 172.30.42.1: icmp_seq=5072 ttl=64 time=26.0 ms 1480 bytes from 172.30.42.1: icmp_seq=5073 ttl=64 time=27.0 ms 1480 bytes from 172.30.42.1: icmp_seq=5074 ttl=64 time=25.6 ms 1480 bytes from 172.30.42.1: icmp_seq=5075 ttl=64 time=26.7 ms 1480 bytes from 172.30.42.1: icmp_seq=5076 ttl=64 time=26.9 ms 1480 bytes from 172.30.42.1: icmp_seq=5077 ttl=64 time=25.0 ms Now if I replace pfifo_fast by fq_codel : (still TSO and GSO are on) 1480 bytes from 172.30.42.1: icmp_seq=37 ttl=64 time=0.197 ms 1480 bytes from 172.30.42.1: icmp_seq=38 ttl=64 time=0.283 ms 1480 bytes from 172.30.42.1: icmp_seq=39 ttl=64 time=0.183 ms 1480 bytes from 172.30.42.1: icmp_seq=40 ttl=64 time=0.182 ms 1480 bytes from 172.30.42.1: icmp_seq=41 ttl=64 time=0.207 ms 1480 bytes from 172.30.42.1: icmp_seq=42 ttl=64 time=0.202 ms 1480 bytes from 172.30.42.1: icmp_seq=43 ttl=64 time=0.244 ms 1480 bytes from 172.30.42.1: icmp_seq=44 ttl=64 time=0.200 ms 1480 bytes from 172.30.42.1: icmp_seq=45 ttl=64 time=0.212 ms 1480 bytes from 172.30.42.1: icmp_seq=46 ttl=64 time=0.215 ms 1480 bytes from 172.30.42.1: icmp_seq=47 ttl=64 time=0.178 ms 1480 bytes from 172.30.42.1: icmp_seq=48 ttl=64 time=0.215 ms 1480 bytes from 172.30.42.1: icmp_seq=49 ttl=64 time=0.238 ms 1480 bytes from 172.30.42.1: icmp_seq=50 ttl=64 time=0.210 ms 1480 bytes from 172.30.42.1: icmp_seq=51 ttl=64 time=0.974 ms 1480 bytes from 172.30.42.1: icmp_seq=52 ttl=64 time=1.93 ms 1480 bytes from 172.30.42.1: icmp_seq=53 ttl=64 time=1.71 ms 1480 bytes from 172.30.42.1: icmp_seq=54 ttl=64 time=3.07 ms 1480 bytes from 172.30.42.1: icmp_seq=55 ttl=64 time=3.47 ms 1480 bytes from 172.30.42.1: icmp_seq=56 ttl=64 time=2.53 ms 1480 bytes from 172.30.42.1: icmp_seq=57 ttl=64 time=3.24 ms 1480 bytes from 172.30.42.1: icmp_seq=58 ttl=64 time=3.11 ms 1480 bytes from 172.30.42.1: icmp_seq=59 ttl=64 time=3.03 ms 1480 bytes from 172.30.42.1: icmp_seq=60 ttl=64 time=2.96 ms 1480 bytes from 172.30.42.1: icmp_seq=61 ttl=64 time=2.90 ms 1480 bytes from 172.30.42.1: icmp_seq=62 ttl=64 time=2.97 ms -- 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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