Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262409AbVC3TI7 (ORCPT ); Wed, 30 Mar 2005 14:08:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262412AbVC3TIw (ORCPT ); Wed, 30 Mar 2005 14:08:52 -0500 Received: from mail.dif.dk ([193.138.115.101]:679 "EHLO mail.dif.dk") by vger.kernel.org with ESMTP id S262409AbVC3TIK (ORCPT ); Wed, 30 Mar 2005 14:08:10 -0500 Date: Wed, 30 Mar 2005 21:10:14 +0200 (CEST) From: Jesper Juhl To: Paul Jackson Cc: Pekka J Enberg , jengelh@linux01.gwdg.de, penberg@gmail.com, rlrevell@joe-job.com, davej@redhat.com, linux-kernel@vger.kernel.org Subject: Re: no need to check for NULL before calling kfree() -fs/ext2/ In-Reply-To: <20050329184411.1faa71eb.pj@engr.sgi.com> Message-ID: References: <1111825958.6293.28.camel@laptopd505.fenrus.org> <1111881955.957.11.camel@mindpipe> <20050327065655.6474d5d6.pj@engr.sgi.com> <20050327174026.GA708@redhat.com> <1112064777.19014.17.camel@mindpipe> <84144f02050328223017b17746@mail.gmail.com> <20050329184411.1faa71eb.pj@engr.sgi.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1594 Lines: 45 On Tue, 29 Mar 2005, Paul Jackson wrote: > Pekka wrote: > > (4) The cleanups Jesper and others are doing are to remove the > > _redundant_ NULL checks (i.e. it is now checked twice). > > Even such obvious changes as removing redundant checks doesn't > seem to ensure a performance improvement. Jesper Juhl posted > performance data for such changes in his microbenchmark a couple > of days ago. > > As I posted then, I could swear that his numbers show: > > > Just looking at the third run, it seems to me that "if (likely(p)) > > kfree(p);" beats a naked "kfree(p);" everytime, whether p is half > > NULL's, or very few NULL's, or almost all NULL's. > > Twice now I have asked Jesper to explain this strange result. > I've been kept busy with other things for a while and haven't had the time to reply to your emails, sorry. As I just said in another post I don't know how valid my numbers are, but I'll try and craft a few more tests to see if I can get some more solid results. > > Maybe we should be following your good advice: > > > You don't know that until you profile! > > instead of continuing to make these code changes. > I'll gather some more numbers and post them along with any conclusions I believe can be drawn from them within a day or two, untill then I'll hold back on the patches... -- Jesper Juhl - 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/