Date: Fri, 16 Jan 2009 11:12:00 +1100
From: Herbert Xu <herbert@gondor.apana.org.au>
To: Ingo Molnar <mingo@elte.hu>
Cc: akpm@linux-foundation.org, tj@kernel.org, hpa@zytor.com, brgerst@gmail.com,
       ebiederm@xmission.com, cl@linux-foundation.org, rusty@rustcorp.com.au,
       travis@sgi.com, linux-kernel@vger.kernel.org, steiner@sgi.com,
       hugh@veritas.com
Subject: Re: [PATCH] percpu: add optimized generic percpu accessors
Message-ID: <20090116001200.GA9137@gondor.apana.org.au>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20090115183942.GA6325@elte.hu>
Organization: Core
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1073
Lines: 29

Ingo Molnar <mingo@elte.hu> wrote:
>
>> Of course.  But do any architectures actually _need_ that for a single 
>> read?
> 
> not for a read i guess - but for the other ops like add/and/or/xor.

One of the things I'd like to see happen with this work is for
us to have a cheap per-cpu atomic counter that we can use for
SNMP stats.

If we can make the inc/add variants into a single instruction,
then it won't need to disable preemption or interrupts.

So if you could design the API such that we have a variant of
add/inc that automatically disables/enables preemption then we
can optimise that away on x86.

Thanks,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/