From: Eric Dumazet <dada1@cosmosbay•com>
To: Christoph Lameter <cl@linux-foundation•org>
Cc: Kenny Chang <kchang@athenacr•com>, netdev@vger•kernel.org
Subject: Re: Multicast packet loss
Date: Fri, 27 Feb 2009 22:36:21 +0100 [thread overview]
Message-ID: <49A85CD5.40404@cosmosbay.com> (raw)
In-Reply-To: <49A84916.9090106@cosmosbay.com>
Eric Dumazet a écrit :
> Christoph Lameter a écrit :
>> On Fri, 27 Feb 2009, Eric Dumazet wrote:
>>
>>> Christoph Lameter a ?crit :
>>>> On Fri, 30 Jan 2009, Eric Dumazet wrote:
>>>>> 2.6.29-rc contains UDP receive improvements (lockless)
>>>>> Problem is multicast handling was not yet updated, but could be :)
>>>> When will that happen?
>>> When proven necessary :)
>>>
>>> Kenny problem is about scheduling storm. The extra spin_lock() in UDP
>>> multicast receive is not a problem.
>> My tests here show that 2.6.29-rc5 still looses ~5usec vs. 2.6.22 via
>> UDP. This would fix a regression.....
>>
>
> Could you elaborate ?
>
> I just retried Kenny test here. As one cpu is looping in ksoftirqd, only this cpu
> touches the spin_lock, so spin_lock()/spin_unlock() is free.
>
> oprofile shows that udp stack is lightweight in this case. Problem is about wakeing up
> so many threads...
>
> CPU: Core 2, speed 3000.16 MHz (estimated)
> Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
> samples cum. samples % cum. % symbol name
> 356857 356857 15.1789 15.1789 schedule
> 274028 630885 11.6557 26.8346 mwait_idle
> 189218 820103 8.0484 34.8829 __skb_recv_datagram
> 116903 937006 4.9725 39.8554 skb_release_data
> 103152 1040158 4.3876 44.2430 lock_sock_nested
> 89600 1129758 3.8111 48.0541 udp_recvmsg
> 74171 1203929 3.1549 51.2089 copy_to_user
> 72299 1276228 3.0752 54.2842 set_next_entity
> 60392 1336620 2.5688 56.8529 sched_clock_cpu
> 54026 1390646 2.2980 59.1509 __slab_free
> 50212 1440858 2.1358 61.2867 prepare_to_wait_exclusive
> 38689 1479547 1.6456 62.9323 cpu_idle
> 38142 1517689 1.6224 64.5547 __switch_to
> 36701 1554390 1.5611 66.1157 hrtick_start_fair
> 36673 1591063 1.5599 67.6756 dst_release
> 36268 1627331 1.5427 69.2183 sys_recvfrom
> 35052 1662383 1.4909 70.7092 kmem_cache_free
> 32680 1695063 1.3900 72.0992 pick_next_task_fair
> 31209 1726272 1.3275 73.4267 try_to_wake_up
> 30382 1756654 1.2923 74.7190 dequeue_task_fair
> 29048 1785702 1.2356 75.9545 __copy_skb_header
> 28801 1814503 1.2250 77.1796 sock_def_readable
> 28655 1843158 1.2188 78.3984 enqueue_task_fair
> 27232 1870390 1.1583 79.5567 update_curr
> 21688 1892078 0.9225 80.4792 copy_from_user
> 18832 1910910 0.8010 81.2802 sysenter_past_esp
> 17732 1928642 0.7542 82.0345 finish_task_switch
> 17583 1946225 0.7479 82.7824 resched_task
> 17367 1963592 0.7387 83.5211 native_sched_clock
> 15691 1979283 0.6674 84.1885 task_rq_lock
> 15352 1994635 0.6530 84.8415 sock_queue_rcv_skb
> 15022 2009657 0.6390 85.4804 udp_queue_rcv_skb
> 13999 2023656 0.5954 86.0759 __update_sched_clock
> 12284 2035940 0.5225 86.5984 skb_copy_datagram_iovec
> 11869 2047809 0.5048 87.1032 release_sock
> 10986 2058795 0.4673 87.5705 __wake_up_sync
> 10488 2069283 0.4461 88.0166 sock_recvmsg
> 9686 2078969 0.4120 88.4286 skb_queue_tail
> 9425 2088394 0.4009 88.8295 sys_socketcall
>
>
My guess is commit 95766fff6b9a78d11fc2d3812dd035381690b55d
(UDP: Add memory accounting)
Hideo Aoki [Mon, 31 Dec 2007 08:29:24 +0000 (00:29 -0800)]
and 3ab224be6d69de912ee21302745ea45a99274dbc
[NET] CORE: Introducing new memory accounting interface.
Date: Mon Dec 31 00:11:19 2007 -0800
are responsible for slowdown, because they add some
lock_sock()/release_sock() pairs.
function udp_recvmsg()
out_free:
+ lock_sock(sk);
skb_free_datagram(sk, skb);
+ release_sock(sk);
out:
I wonder why we can call __sk_mem_reclaim() when dequeing *one* UDP
frame in queue, while many others can still be in sk_receive_queue.
This defeats memory accounting, no ?
We should avoid lock_sock() if possible, or risk delaying
softirq RX in udp_queue_rcv_skb()
next prev parent reply other threads:[~2009-02-27 21:37 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-30 17:49 Multicast packet loss Kenny Chang
2009-01-30 19:04 ` Eric Dumazet
2009-01-30 19:17 ` Denys Fedoryschenko
2009-01-30 20:03 ` Neil Horman
2009-01-30 22:29 ` Kenny Chang
2009-01-30 22:41 ` Eric Dumazet
2009-01-31 16:03 ` Neil Horman
2009-02-02 16:13 ` Kenny Chang
2009-02-02 16:48 ` Kenny Chang
2009-02-03 11:55 ` Neil Horman
2009-02-03 15:20 ` Kenny Chang
2009-02-04 1:15 ` Neil Horman
2009-02-04 16:07 ` Kenny Chang
2009-02-04 16:46 ` Wesley Chow
2009-02-04 18:11 ` Eric Dumazet
2009-02-05 13:33 ` Neil Horman
2009-02-05 13:46 ` Wesley Chow
2009-02-05 13:29 ` Neil Horman
2009-02-01 12:40 ` Eric Dumazet
2009-02-02 13:45 ` Neil Horman
2009-02-02 16:57 ` Eric Dumazet
2009-02-02 18:22 ` Neil Horman
2009-02-02 19:51 ` Wes Chow
2009-02-02 20:29 ` Eric Dumazet
2009-02-02 21:09 ` Wes Chow
2009-02-02 21:31 ` Eric Dumazet
2009-02-03 17:34 ` Kenny Chang
2009-02-04 1:21 ` Neil Horman
2009-02-26 17:15 ` Kenny Chang
2009-02-28 8:51 ` Eric Dumazet
2009-03-01 17:03 ` Eric Dumazet
2009-03-04 8:16 ` David Miller
2009-03-04 8:36 ` Eric Dumazet
2009-03-07 7:46 ` Eric Dumazet
2009-03-08 16:46 ` Eric Dumazet
2009-03-09 2:49 ` David Miller
2009-03-09 6:36 ` Eric Dumazet
2009-03-13 21:51 ` David Miller
2009-03-13 22:30 ` Eric Dumazet
2009-03-13 22:38 ` David Miller
2009-03-13 22:45 ` Eric Dumazet
2009-03-14 9:03 ` [PATCH] net: reorder fields of struct socket Eric Dumazet
2009-03-16 2:59 ` David Miller
2009-03-16 22:22 ` Multicast packet loss Eric Dumazet
2009-03-17 10:11 ` Peter Zijlstra
2009-03-17 11:08 ` Eric Dumazet
2009-03-17 11:57 ` Peter Zijlstra
2009-03-17 15:00 ` Brian Bloniarz
2009-03-17 15:16 ` Eric Dumazet
2009-03-17 19:39 ` David Stevens
2009-03-17 21:19 ` Eric Dumazet
2009-04-03 19:28 ` Brian Bloniarz
2009-04-05 13:49 ` Eric Dumazet
2009-04-06 21:53 ` Brian Bloniarz
2009-04-06 22:12 ` Brian Bloniarz
2009-04-07 20:08 ` Brian Bloniarz
2009-04-08 8:12 ` Eric Dumazet
2009-03-09 22:56 ` Brian Bloniarz
2009-03-10 5:28 ` Eric Dumazet
2009-03-10 23:22 ` Brian Bloniarz
2009-03-11 3:00 ` Eric Dumazet
2009-03-12 15:47 ` Brian Bloniarz
2009-03-12 16:34 ` Eric Dumazet
2009-02-27 18:40 ` Christoph Lameter
2009-02-27 18:56 ` Eric Dumazet
2009-02-27 19:45 ` Christoph Lameter
2009-02-27 20:12 ` Eric Dumazet
2009-02-27 21:36 ` Eric Dumazet [this message]
2009-02-02 13:53 ` Eric Dumazet
-- strict thread matches above, loose matches on Subject: below --
2009-04-05 14:42 bmb
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