linux-kernel - Re: bad networking related lag in v2.6.22-rc2

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Date:	Mon, 21 May 2007 12:09:40 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	kernel@...chanda.info, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	tglx@...utronix.de
Subject: Re: bad networking related lag in v2.6.22-rc2

* David Miller <davem@...emloft.net> wrote:

> >  gkrellm-5977 0..s.  0us : cond_resched_softirq 
> >  (established_get_next)
> 
> So it's not the 3c59x bug :-)
> 
> If you have a lot of sockets, there is not way to make the performance 
> of dumping /proc/net/tcp not suck, use the netlink socket dumping 
> which is:
> 
> 1) more efficient even for full dumps
> 2) allows filtering for the best possible performance

hm, there is a cond_resched_softirq() for every line output so the 
actual latency from this alone shouldnt be that bad. While /proc/net/tcp 
has a quadratic algorithm, the per-line latency is O(N), which shouldnt 
show up on the radar.

but note that Ananitya is running a fast system as a stock desktop 
system browsing the web, so there shouldnt be tons of sockets. So the 
latency isnt caused by /proc/net/tcp itself, but there does seem to be 
some networking related anomaly.

we'll hopefully be able to tell this more specifically from the re-done 
trace.

	Ingo
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