linux-kernel - Re: [RFC][PATCH 1/7] Resource counters

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Message-ID: <45F7A04B.6000504@sw.ru>
Date:	Wed, 14 Mar 2007 10:12:11 +0300
From:	Pavel Emelianov <xemul@...ru>
To:	vatsa@...ibm.com
CC:	Herbert Poetzl <herbert@...hfloor.at>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	containers@...ts.osdl.org, Paul Menage <menage@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/7] Resource counters

Srivatsa Vaddagiri wrote:
> On Tue, Mar 13, 2007 at 06:41:05PM +0300, Pavel Emelianov wrote:
>>> right, but atomic ops have much less impact on most
>>> architectures than locks :)
>> Right. But atomic_add_unless() is slower as it is
>> essentially a loop. See my previous letter in this sub-thread.
> 
> If I am not mistaken, you shouldn't loop in normal cases, which means
> it boils down to a atomic_read() + atomic_cmpxch()
> 
> 

So does the lock - in a normal case (when it's not
heavily contented) it will boil down to atomic_dec_and_test().

Nevertheless, making charge like in this patchset
requires two atomic ops with atomic_xxx and only
one with spin_lock().
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