Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression

Eric Dumazet
2007-09-30T17:49:08Z

Denys a écrit :
> I've moved recently one of my proxies(squid and some compressing application)
> from 2.6.21 to 2.6.22, and notice huge performance drop. I think this is
> important, cause it can cause serious regression on some other workloads like
> busy web-servers and etc.
>
> After some analysis of different options i can bring more exact numbers:
>
> 2.6.21 able to process 500-550 requests/second and 15-20 Mbit/s of traffic,
> and working great without any slowdown or instability.
>
> 2.6.22 able to process only 250-300 requests and 8-10 Mbit/s of traffic, ssh
> and console is "freezing" (there is delay even for typing characters).
>
> Both proxies is on identical hardware(Sun Fire X4100), configuration(small
> system, LFS-like, on USB flash), different only kernel.
>
> I tried to disable/enable various options and optimisations - it doesn't
> change anything, till i reach SLUB/SLAB option.
>
> I've loaded proxy configuration to gentoo PC with 2.6.22 (then upgraded it to
> 2.6.23-rc8), and having same effect.
> Additionally, when load reaching maximum i can notice whole system slowdown,
> for example ssh and scp takes much more time to run, even i do nice -n -5 for
> them.
>
> But even choosing 2.6.23-rc8+SLAB i noticed same "freezing" of ssh (and sure
> it slowdown other kind of network performance), but much less comparing with
> SLUB. On top i am seeing ksoftirqd taking almost 100% (sometimes ksoftirqd/0,
> sometimes ksoftirqd/1).
>
> I tried also different tricks with scheduler (/proc/sys/kernel/sched*), but
> it's also didn't help.
>
> When it freezes it looks like:
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 7 root 15 -5 0 0 0 R 64 0.0 2:47.48 ksoftirqd/1
> 5819 root 20 0 134m 130m 596 R 57 3.3 4:36.78 globax
> 5911 squid 20 0 1138m 1.1g 2124 R 26 28.9 2:24.87 squid
> 10 root 15 -5 0 0 0 S 1 0.0 0:01.86 events/1
> 6130 root 20 0 3960 2416 1592 S 0 0.1 0:08.02 oprofiled
>
>
> Oprofile results:
>
>
> Thats oprofile with 2.6.23-rc8 - SLUB
>
> 73918 21.5521 check_bytes
> 38361 11.1848 acpi_pm_read
> 14077 4.1044 init_object
> 13632 3.9747 ip_send_reply
> 8486 2.4742 __slab_alloc
> 7199 2.0990 nf_iterate
> 6718 1.9588 page_address
> 6716 1.9582 tcp_v4_rcv
> 6425 1.8733 __slab_free
> 5604 1.6339 on_freelist
>
>
> Thats oprofile with 2.6.23-rc8 - SLAB
>
> CPU: AMD64 processors, speed 2592.64 MHz (estimated)
> Counted CPU_CLK_UNHALTED events (Cycles outside of halt state) with a unit
> mask of 0x00 (No unit mask) count 100000
> samples % symbol name
> 138991 14.0627 acpi_pm_read
> 52401 5.3018 tcp_v4_rcv
> 48466 4.9037 nf_iterate
> 38043 3.8491 __slab_alloc
> 34155 3.4557 ip_send_reply
> 20963 2.1210 ip_rcv
> 19475 1.9704 csum_partial
> 19084 1.9309 kfree
> 17434 1.7639 ip_output
> 17278 1.7481 netif_receive_skb
> 15248 1.5428 nf_hook_slow
>
> My .config is at http://www.nuclearcat.com/.config (there is SPARSEMEM
> enabled, it doesn't make any noticeable difference)
>
> Please CC me on reply, i am not in list.
>

Could you try with SLUB but disabling CONFIG_SLUB_DEBUG ?