From: Andi Kleen <ak@suse.de>
To: Christoph Lameter <clameter@sgi.com>
Cc: linux-arch@vger.kernel.org
Subject: Re: Better local_t implementation needed
Date: Fri, 20 Apr 2007 19:01:39 +0200 [thread overview]
Message-ID: <200704201901.39437.ak@suse.de> (raw)
In-Reply-To: <Pine.LNX.4.64.0704200903130.20232@schroedinger.engr.sgi.com>
On Friday 20 April 2007 18:10:32 Christoph Lameter wrote:
>
> > Using local_t for per cpu counters is nice because then
> > one can use cpu_local_add() etc. and that generates very good
> > code at least on x86 and a few other architectures. That would
> > then allow very cheap per CPU statistics, which are useful
> > in a number of subsystems (like networking or MM code)
>
> Is the per cpu access fixed on x86? Last I checked it was not atomic.
With upcomming patches per cpu can be directly referenced using %fs/%gs
Then cpu_local_add() etc will be a single instruction that is atomic
regarding interrupts.
> Uhhh.... Yuck.
>
> > Drawback will be larger code.
>
> Fix the per cpu area access instead?
That doesn't help on architectures that don't have r-m-w instructions
on memory (like all RISCSs)
-Andi
next prev parent reply other threads:[~2007-04-20 17:04 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-20 10:56 Better local_t implementation needed Andi Kleen
2007-04-20 16:10 ` Christoph Lameter
2007-04-20 17:01 ` Andi Kleen [this message]
2007-04-20 17:05 ` Christoph Lameter
2007-04-20 18:31 ` Luck, Tony
2007-04-20 20:14 ` Andi Kleen
2007-04-20 20:27 ` Christoph Lameter
2007-04-20 21:25 ` Roman Zippel
2007-04-20 22:39 ` David Miller
2007-04-21 0:25 ` Christoph Lameter
2007-04-21 4:45 ` David Miller
[not found] <617E1C2C70743745A92448908E030B2A015F2392@scsmsx411.amr.corp.intel.com>
2007-04-20 20:38 ` Christoph Lameter
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