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

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Message-Id: <20080827.150955.118944272.davem@davemloft.net>
Date:	Wed, 27 Aug 2008 15:09:55 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
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

From: Stephen Hemminger <shemminger@...tta.com>
Date: Wed, 27 Aug 2008 14:48:00 -0700

> I do wonder if having large hash table actually helps? When TCP hash
> table gets too big, it means every lookup is a cache miss. Assuming
> a busy server with 2000 connections and perfect hash. On a 4G mem x86-64
> we are doing 512K hash entries which is ridiculous. Something like 64K
> entries is more than enough.

That's true, but it's nearly guaranteed to only be a single cache miss
at worst (if the hash function is working) compared to potentially
multiple ones if we sized it too small.

I really see the only way to move forward is to dynamically size the
thing.  And nobody has been strong enough to implement that yet :)
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