2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression

From: Denys
Date: Sun Sep 30 2007 - 13:31:47 EST

I tried changing clocksource from acpi_pm to tsc. No difference.
Tried to lock eth0 by smp_affinity to single CPU (no other interrups, except
ioapic timer(LOC) there). No luck. I tried to change hashes in nf_conntrack,
no difference. Tried to change eth0 weidht - no difference.

Also i notice, that exactly when softirqd start using CPU nearby 100% -
problems happens.

At this time (with or without nice - the same, also the same to ping any host
in network)

defaulthost ~ #nice -n -10 ping -s 10000
PING ( 10000(10028) bytes of data.

10008 bytes from icmp_seq=1 ttl=64 time=377 ms
10008 bytes from icmp_seq=2 ttl=64 time=328 ms
10008 bytes from icmp_seq=3 ttl=64 time=329 ms
10008 bytes from icmp_seq=4 ttl=64 time=355 ms
10008 bytes from icmp_seq=5 ttl=64 time=0.047 ms

Delay value is ALWAYS nearby same. 350-360ms.

At same time if i ping "buggy 2.6.23-rc8" box, ping delay is perfect.

100000 packets transmitted, 100000 received, 0% packet loss, time 41793ms
rtt min/avg/max/mdev = 0.027/0.127/1.439/0.095 ms, ipg/ewma 0.417/0.065 ms

There is nothing running except:
squid, globax (TCP accelerator).
Logs, disk cache on squid is disabled.
Important note - there is conntract and REDIRECT used.

defaulthost /config #cat /proc/net/sockstat
sockets: used 10670
TCP: inuse 12734 orphan 1390 tw 20248 alloc 12751 mem 9903
UDP: inuse 5
UDPLITE: inuse 0
RAW: inuse 0
FRAG: inuse 0 memory 0

defaulthost /config #cat /proc/net/softnet_stat
96c0060c 00000000 003fa90a 00000000 00000000 00000000 00000000 00000000
926120af 00000000 003e8692 00000000 00000000 00000000 00000000 00000000

defaulthost /config #cat /proc/net/ip_conntrack|wc -l
(other host running 200K easily)

What can cause delays ~350-360ms for userspace applications?

Denys Fedoryshchenko
Technical Manager
Virtual ISP S.A.L.

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