From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763553AbYDVT0k (ORCPT ); Tue, 22 Apr 2008 15:26:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757309AbYDVT03 (ORCPT ); Tue, 22 Apr 2008 15:26:29 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:53544 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757237AbYDVT02 (ORCPT ); Tue, 22 Apr 2008 15:26:28 -0400 Date: Tue, 22 Apr 2008 21:26:01 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Jens Axboe , linux-arch@vger.kernel.org, Linux Kernel Mailing List , npiggin@suse.de, peterz@infradead.org, sam@ravnborg.org Subject: Re: [PATCH 2/11] x86: convert to generic helpers for IPI function calls Message-ID: <20080422192601.GB12588@elte.hu> References: <1208890227-24808-1-git-send-email-jens.axboe@oracle.com> <1208890227-24808-3-git-send-email-jens.axboe@oracle.com> <20080422191213.GA6370@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Linus Torvalds wrote: > > yes and i gave in - Nick and Jens wants to do some crazy stuff and > > they had the numbers. Here's the previous discussion: > > > > http://lkml.org/lkml/2008/2/27/125 > > No, the previous discussion was about single *queues* vs single > *vectors*. > > I agree unconditionally with the decision to use a separate per-cpu > queue from the shared queue (in fact, I would argue that the "mask" > code might want to notice when the mask is just a single CPU, and turn > a mask request into a targeted request). > > But I wonder why we want to then have two IPI target vectors, when it > would appear to be perfectly fine and cheap to have just a single > vector that can handle both the per-cpu case and the shared queue case > (since the thing would tend to be one or the other, not both). > > A single vector is still pefectly fine, if 99% of all usage cases are > the targeted-to-a-single-cpu thing, because the shared queue will > basically be empty (and you can test that without even taking any > locks). ok. In which case the reschedule vector could be consolidated into that as well (it's just a special single-CPU call). Then there would be no new vector allocations needed at all, just the renaming of RESCHEDULE_VECTOR to something more generic. Ingo