Re: Strange latency spikes/TX network stalls on Sun Fire X4150(x86) and e1000e

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

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


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