Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761834AbXFRK6h (ORCPT ); Mon, 18 Jun 2007 06:58:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760106AbXFRK6a (ORCPT ); Mon, 18 Jun 2007 06:58:30 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:44067 "EHLO ecfrec.frec.bull.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755015AbXFRK63 (ORCPT ); Mon, 18 Jun 2007 06:58:29 -0400 Message-ID: <46766552.3080803@bull.net> Date: Mon, 18 Jun 2007 12:58:26 +0200 From: Pierre Peiffer User-Agent: Thunderbird 2.0.0.0 (X11/20070419) MIME-Version: 1.0 To: Thomas Gleixner Cc: Linus Torvalds , LKML , Ingo Molnar , Andrew Morton , Ulrich Drepper , Jakub Jelinek Subject: Re: [PATCH] Futex: Revert the non-functional REQUEUE_PI References: <1182107470.8176.455.camel@chaos> In-Reply-To: <1182107470.8176.455.camel@chaos> X-MIMETrack: Itemize by SMTP Server on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 18/06/2007 13:02:19, Serialize by Router on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 18/06/2007 13:02:21, Serialize complete at 18/06/2007 13:02:21 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-15; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1817 Lines: 49 Thomas Gleixner wrote : > Patch d0aa7a70bf03b9de9e995ab272293be1f7937822 titled > > "futex_requeue_pi optimization" > > introduced user space visible changes to the futex syscall. > > The patch is non-functional and there is no way to fix it proper before > the 2.6.22 release. > > The breakage report ( http://lkml.org/lkml/2007/5/12/17 ) went > unanswered, Sorry, but I passed lot of time on this last year without any answers or comments from the community when I have sent my patches. Now I'm working on something else and I can't spent more time on this for now... Futexes are so complex that it is always difficult to investigate a problem in only one or two hours... > and unfortunately it turned out that the concept is not > feasible at all. Without robust futex, the concept works well, and the performance gain has been proven. It violates the rtmutex semantics badly by introducing > a virtual owner, which hacks around the coupling of the user-space > pi_futex and the kernel internal rt_mutex representation. What you call a hack, is for me a design point. And if this is a hack, then I think that we can say that futexes are based on a series of hacks... But, okay, this is not very constructive, so... Ulrich Drepper wrote : > > Indeed. A lot more discussion is needed to handle this correctly. No > committed code in glibc so far uses the function so removal is no problem. Once again, it's a pity that people didn't spent time to comment on this when I was working on this. Now, the work will probably just be lost... -- Pierre - 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/