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

Eric Dumazet
2007-10-01T05:59:42Z

Denys a écrit :
> Hi
>
> I got
>
> pi linux-git # git bisect bad
> Bisecting: 0 revisions left to test after this
> [f85958151900f9d30fa5ff941b0ce71eaa45a7de] [NET]: random functions can use
> nsec resolution instead of usec
>
> I will make sure and will try to reverse this patch on 2.6.22
>
> But it seems "that's it".

Well... thats interesting...

No problem here on bigger servers, so I CC David Miller and netdev on this one.

AFAIK do_gettimeofday() and ktime_get_real() should use the same underlying
hardware functions on PC and no performance problem should happen here.

(relevant part of this patch :

@ -1521,7 +1515,6 @@ __u32 secure_ip_id(__be32 daddr)
__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
__be16 sport, __be16 dport)
{
- struct timeval tv;
__u32 seq;
__u32 hash[4];
struct keydata *keyptr = get_keyptr();
@@ -1543,12 +1536,11 @@ __u32 secure_tcp_sequence_number(__be32 saddr, __be32
daddr,
* As close as possible to RFC 793, which
* suggests using a 250 kHz clock.
* Further reading shows this assumes 2 Mb/s networks.
- * For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
+ * For 10 Gb/s Ethernet, a 1 GHz clock is appropriate.
* That's funny, Linux has one built in! Use it!
* (Networks are faster now - should this be increased?)
*/
- do_gettimeofday(&tv);
- seq += tv.tv_usec + tv.tv_sec * 1000000;
+ seq += ktime_get_real().tv64;

Thank you for doing this research.

>
>
> On Sun, 30 Sep 2007 14:25:37 +1000, Nick Piggin wrote
>> Hi Denys, thanks for reporting (btw. please reply-to-all when
>> replying on lkml).
>>
>> You say that SLAB is better than SLUB on an otherwise identical
>> kernel, but I didn't see if you quantified the actual numbers? It
>> sounds like there is still a regression with SLAB?
>>
>> On Monday 01 October 2007 03:48, Eric Dumazet wrote:
>>> Denys a :
>>>> 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 ?
>
>
> --
> Denys Fedoryshchenko
> Technical Manager
> Virtual ISP S.A.L.
>
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