Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression
From: Eric Dumazet
Date: Mon Oct 01 2007 - 01:59:46 EST
Denys a Ãcrit :
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.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/