Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757221Ab2BBVAY (ORCPT ); Thu, 2 Feb 2012 16:00:24 -0500 Received: from mail-gx0-f174.google.com ([209.85.161.174]:62523 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754183Ab2BBVAW convert rfc822-to-8bit (ORCPT ); Thu, 2 Feb 2012 16:00:22 -0500 MIME-Version: 1.0 In-Reply-To: <20120202121912.c82a185e.akpm@linux-foundation.org> References: <1328055439-9441-1-git-send-email-venki@google.com> <20120201140125.c656df41.akpm@linux-foundation.org> <87d39xj955.fsf@rustcorp.com.au> <20120202121912.c82a185e.akpm@linux-foundation.org> Date: Thu, 2 Feb 2012 13:00:21 -0800 Message-ID: Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 From: Venki Pallipadi To: Andrew Morton Cc: Rusty Russell , KOSAKI Motohiro , KOSAKI Motohiro , Mike Travis , "Srivatsa S. Bhat" , "Paul E. McKenney" , "Rafael J. Wysocki" , Paul Gortmaker , linux-kernel@vger.kernel.org X-System-Of-Record: true Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1972 Lines: 54 On Thu, Feb 2, 2012 at 12:19 PM, Andrew Morton wrote: > On Fri, 03 Feb 2012 06:33:02 +1030 > Rusty Russell wrote: > >> On Wed, 1 Feb 2012 14:01:25 -0800, Andrew Morton wrote: >> > > Though most of the callers of these two routines are init time (with few >> > > exceptions of runtime calls), it is cleaner to use variables >> > > and not go through this repeated mask based calculation. >> > >> > Looks good to me. >> >> But, I wonder who's asking num_possible_cpus(). ?It's not a very useful >> thing to know, though some arch's "know" it's contiguous, so can cheat. >> >> Optimizing it seems particularly foolish. > > We're fools for optimisations! > I would think that if we are giving an API people will abuse it sooner or later :-). >> We either audit and wean >> everyone off who's using it incorrectly, or insist on contiguous CPU >> numbers and drop the mask altogether. > > drivers/block/nvme.c looks like it's assuming a contiguous map. ?Maybe > also drivers/scsi/bnx2fc (wtf?). ?I didn't see anything else outside > arch code. > Yes. I found a bunch of them which seemed obviously wrong. Doing things like allocating space based on num_possible_cpus() and accessing the space with get_cpu() or doing cou_online() check etc. arch/x86/kernel/apic/x2apic_uv_x.c arch/x86/kernel/cpu/mcheck/mce-inject.c arch/x86/platform/uv/tlb_uv.c drivers/scsi/bnx2fc/bnx2fc_io.c kernel/debug/kdb/kdb_bt.c I have a patch to fix these obvious ones. But, there are other users which were not very obvious to me and also I am know of code in older kernels (code which since have been rewritten) which can get benefit of this API change. Thanks, Venki -- 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/