netdev - Re: cat /proc/net/tcp takes 0.5 seconds on x86

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Date:	Thu, 28 Aug 2008 01:09:19 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Miller <davem@...emloft.net>
Cc:	andi@...stfloor.org, davej@...hat.com, netdev@...r.kernel.org,
	j.w.r.degoede@....nl
Subject: Re: cat /proc/net/tcp takes 0.5 seconds on x86_64

David Miller a écrit :
> From: Andi Kleen <andi@...stfloor.org>
> Date: Thu, 28 Aug 2008 00:34:10 +0200
> 
>> It fixes an old performance problem at least. I'm not aware 
>> of any new ones in this area because the code in this 
>> function hasn't changed since I last looked.
> 
> That's exactly what this thread is about, things got slower for
> some reason even though nothing specifically changed in this area.
> 
> I wonder if indirectly something changed in how the hash table
> allocator code down in mm/*.c works, perhaps it's taking NUMA
> into account differently now?
> 

Not really, I suspect commit (a7ab4b501f9b8a9dc4d5cee542db67b6ccd1088b 
[TCPv4]: Improve BH latency in /proc/net/tcp) is responsible for longer delays.
Note that its rather old :
Date:   Sun Jun 10 17:33:08 2007 -0700

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.

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

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