lkml.org 
[lkml]   [2008]   [Jan]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: questions on NAPI processing latency and dropped network packets
Chris Friesen a écrit :
> Eric Dumazet wrote:
>> Chris Friesen a écrit :
>
>>> Based on profiling and instrumentation it seems like the cost of
>>> sctp_endpoint_lookup_assoc() more than triples, which means that the
>>> amount of time that bottom halves are disabled in that function also
>>> triples.
>>
>> Any idea of the size of sctp hash size you have ?
>> (your dmesg probably includes a message starting with SCTP: Hash
>> tables configured...
>> How many concurrent sctp sockets are handled ?
>
> Our lab is currently rebooting, but I'll try and get this once it's
> back up.
>
>> Maybe sctp_assoc_hashfn() is too weak for your use, and some chains
>> are *really* long.
>
> Based on the profiling information we're spending time in
> sctp_endpoint_lookup_assoc() which doesn't actually use hashes, so I
> can't see how the hash would be related. I'm pretty new to SCTP
> though, so I may be missing something.
Well, it does use hashes :)

hash = sctp_assoc_hashfn(ep->base.bind_addr.port, rport);
head = &sctp_assoc_hashtable[hash];
read_lock(&head->lock);
sctp_for_each_hentry(epb, node, &head->chain) {
/* maybe your machine is traversing here a *really* long
chain */
}

>
> Here's the top results from readprofile, unfortunately these are
> aggregated across both cpus so they don't really show what's going on.
> The key thing is that sctp_endpoint_lookup_assoc() is the most
> expensive kernel routine on this entire system.
>
> 3147 .power4_idle 22.4786
> 1712 .native_idle 20.3810
> 1234 .sctp_endpoint_lookup_assoc 2.1725

> 1212 ._spin_unlock_irqrestore 6.4468
> 778 .do_futex 0.3791
> 447 ._spin_unlock_irq 4.2981
> 313 .fget 1.7784
> 277 .fput 3.8472
> 275 .kfree 0.7473
> 234 .__kmalloc 0.5571
> 131 SystemCall_common 0.3411
> 130 .sctp_assoc_is_match 0.6373
> 123 .lock_sock 0.4155
> 119 .find_vma 0.6919
> 116 .kmem_cache_alloc 0.3580
> 111 .kmem_cache_free 0.3343
> 106 .skb_release_data 0.4907
> 102 .__copy_tofrom_user 0.0724
> 100 .exit_elf_binfmt 1.9231
> 100 .do_select 0.0820
>
>
> Chris
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>




--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2008-01-14 20:37    [W:0.125 / U:1.356 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site