netdev - Re: SO_REUSEPORT - can it be done in kernel?

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Date:	Tue, 01 Mar 2011 14:52:46 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Thomas Graf <tgraf@...radead.org>,
	David Miller <davem@...emloft.net>, rick.jones2@...com,
	therbert@...gle.com, wsommerfeld@...gle.com,
	daniel.baluta@...il.com, netdev@...r.kernel.org
Subject: Re: SO_REUSEPORT - can it be done in kernel?

Le mardi 01 mars 2011 à 21:18 +0800, Herbert Xu a écrit :

> Interesting.  So I wonder which lock is showing up at the top
> of the profile with a single socket then.  As it's definitely
> going away with multiple sockets, that means it's not the TX
> queue lock.
> 

This CPU also runs named process, so this is socket lock and receive
queue lock.

Named threads all do : recvmsg()/sendmsg() in a loop, so all are waiting
a frame before doing some work.

Because of single receive queue, extra context switches occur (all
threads but one have to sleep again per query)

For about 80 kqps (standard linux-2.6 kernel, no patches), I have
following vmstat output

procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 4  1      0 2184048  63496 1595056    0    0     0  2060 64592 294528 19 11 67  4
 6  1      0 2184040  63496 1595056    0    0     0  1960 64686 293928 19 11 66  4
 3  1      0 2184040  63496 1595056    0    0     0  2344 64556 294268 20 11 66  4
 4  1      0 2184040  63496 1595056    0    0     0  2400 64626 293859 19 11 67  4



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