linux-kernel - Re: [PATCH 1/2] lib: Provide generic atomic64

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Message-ID: <4A34E4A5.3040306@redhat.com>
Date:	Sun, 14 Jun 2009 14:53:09 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
	akpm@...ux-foundation.org, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lib: Provide generic atomic64_t implementation

Linus Torvalds wrote:
> On Sat, 13 Jun 2009, Linus Torvalds wrote:
>   
>> On Sat, 13 Jun 2009, Paul Mackerras wrote:
>>     
>>> Linus, Andrew: OK if this goes in via the powerpc tree?
>>>       
>> Ok by me.
>>     
>
> Btw, do 32-bit architectures really necessarily want 64-bit performance 
> counters? 
>
> I realize that 32-bit counters will overflow pretty easily, but I do 
> wonder about the performance impact of doing things like hashed spinlocks 
> for 64-bit counters. Maybe the downsides of 64-bit perf counters on such 
> architectures might outweight the upsides?
>   

An alternative implementation using 64-bit cmpxchg will recover most of 
the costs of hashed spinlocks.  I assume most serious 32-bit 
architectures have them?

-- 
error compiling committee.c: too many arguments to function

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