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From: David Miller <davem@davemloft.net>
Subject: Re: cat /proc/net/tcp takes 0.5 seconds on x86_64
Date: Wed, 27 Aug 2008 16:15:04 -0700 (PDT)
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From: Eric Dumazet <dada1@cosmosbay.com>
Date: Thu, 28 Aug 2008 01:09:19 +0200

> Not really, I suspect commit (a7ab4b501f9b8a9dc4d5cee542db67b6ccd1088b [TCPv4]: Improve BH latency in /proc/net/tcp) is responsible for longer delays.
> Note that its rather old :
 ...
> We used to disable bh once, while reading the table. This sucked.
> 
> In case machine is handling trafic, we now are preemptable by softirqs
> while reading /proc/net/tcp. Thats a good thing.

Yes, that would account for it, good spotting.

> By the way, I find Andi patch usefull. Same thing could be done for /proc/net/rt_cache.

Fair enough.  If you can cook up a quick rt_cache patch I'll toss it and
Andi's patch into net-next so it can cook for a while.