linux-kernel - Re: [PATCH] Improve kconfig symbol hashing

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Message-ID: <4B545262.4020907@suse.cz>
Date:	Mon, 18 Jan 2010 13:21:54 +0100
From:	Michal Marek <mmarek@...e.cz>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	zippel@...ux-m68k.org, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Improve kconfig symbol hashing

On 13.1.2010 17:02, Andi Kleen wrote:
[...]
> This patch increases the hash table size to a larger prime
> and switches to a FNV32 hash. I played around with a couple of hash
> functions, but that one seemed to perform best with reasonable
> hash table sizes. 
> 
> Increasing the hash table size even further didn't
> seem like a good idea, because there are a couple of global
> walks which walk the complete hash table.
> 
> I also moved the unnamed bucket to 0. It's still the longest
> of all the buckets (44 entries), but hopefully it's not
> often hit except for the global walk which doesn't care.
> 
> The result is a much nicer distribution:
> (first column bucket length, second number of buckets with that length)
> 
> 1: 3505
> 2: 1236
> 3: 294
> 4: 52
> 5: 3
> 47: 1		<--- this is the unnamed symbols bucket
> 
> There are still some 5+ buckets, but increasing the hash table
> even more would be likely not worth it.
> 
> This also cleans up the code slightly by removing hard coded
> magic numbers.
> 
> I didn't notice a big performance difference either way 
> on my Nehalem system, but I presume it'll help somewhat
> on slower systems.
> 
> ---
>  scripts/kconfig/expr.h              |    5 ++---
>  scripts/kconfig/symbol.c            |   29 +++++++++++++++++------------
>  scripts/kconfig/zconf.tab.c_shipped |    2 +-
>  scripts/kconfig/zconf.y             |    2 +-
>  4 files changed, 21 insertions(+), 17 deletions(-)

Hi Andi,

The patch looks ok, but you forgot your Signed-off-by line?

Michal
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