From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757418AbYDZG3A (ORCPT ); Sat, 26 Apr 2008 02:29:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751875AbYDZG2t (ORCPT ); Sat, 26 Apr 2008 02:28:49 -0400 Received: from gw.goop.org ([64.81.55.164]:54652 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751835AbYDZG2s (ORCPT ); Sat, 26 Apr 2008 02:28:48 -0400 Message-ID: <4812CB99.1070600@goop.org> Date: Fri, 25 Apr 2008 23:28:41 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.12 (X11/20080418) MIME-Version: 1.0 To: Jens Axboe CC: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, npiggin@suse.de, torvalds@linux-foundation.org, peterz@infradead.org, sam@ravnborg.org, Jes Sorensen Subject: Re: [PATCH 1/11] Add generic helpers for arch IPI function calls References: <1208890227-24808-1-git-send-email-jens.axboe@oracle.com> <1208890227-24808-2-git-send-email-jens.axboe@oracle.com> <20080424220157.GA26179@flint.arm.linux.org.uk> <20080425071823.GF12774@kernel.dk> In-Reply-To: <20080425071823.GF12774@kernel.dk> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jens Axboe wrote: > On Thu, Apr 24 2008, Russell King wrote: > >> On Tue, Apr 22, 2008 at 08:50:17PM +0200, Jens Axboe wrote: >> >>> + data->csd.func(data->csd.info); >>> + >>> + spin_lock(&data->lock); >>> + cpu_clear(cpu, data->cpumask); >>> + WARN_ON(data->refs == 0); >>> + data->refs--; >>> + refs = data->refs; >>> >> Probably a silly question, but what does data->refs do that >> cpus_empty(data->cpumask) wouldn't do? (as indeed ARM presently does.) >> > > I guess it can be marginally slower for NR_CPUS > BITS_PER_LONG, > otherwise there's absolutely no reason to have a seperate ref counter. > Jes was concerned about scanning bitmasks on a 4096 CPU Altix. I'm not sure its all that important, but a refcount check would definitely be quicker. J