Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753942AbZA2SJV (ORCPT ); Thu, 29 Jan 2009 13:09:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753637AbZA2SJI (ORCPT ); Thu, 29 Jan 2009 13:09:08 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:45870 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753279AbZA2SJG (ORCPT ); Thu, 29 Jan 2009 13:09:06 -0500 Date: Thu, 29 Jan 2009 10:08:23 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Steven Rostedt cc: Peter Zijlstra , Andrew Morton , LKML , Rusty Russell , npiggin@suse.de, Ingo Molnar , Thomas Gleixner , Arjan van de Ven , jens.axboe@oracle.com Subject: Re: [PATCH -v2] use per cpu data for single cpu ipi calls In-Reply-To: Message-ID: References: <200901290955.38940.rusty@rustcorp.com.au> <20090128173039.cbc29e81.akpm@linux-foundation.org> <1233218954.7835.11.camel@twins> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1121 Lines: 34 On Thu, 29 Jan 2009, Steven Rostedt wrote: > > Actually, we are locking against the destination CPU. Oh. THAT'S JUST INCOMPETENT. What the *fuck* is the point of having per-CPU data, and then using it for the wrong CPU? Stop doing that idiocy. Put the per-cpu data on the senders side, and stop the idiocy. You are going to get cross-CPU cacheline bouncing anyway, there's no way to avoid it, but as long as you do it on the wrong CPU's local data, you're missing the whole POINT of having per-cpu data in the first place. But yeah, that explains the locking. One stupid design mistake leads to another. And are you really sure it cannot be called from within interrupts? I'm finding a lot of callers of smp_call_function_single(), and while I couldn't find any that look like interrupts, I also couldn't find any indication that it never happens. Linus -- 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/