From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754801AbYEaEin (ORCPT ); Sat, 31 May 2008 00:38:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750914AbYEaEif (ORCPT ); Sat, 31 May 2008 00:38:35 -0400 Received: from mx1.redhat.com ([66.187.233.31]:51659 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750889AbYEaEie (ORCPT ); Sat, 31 May 2008 00:38:34 -0400 Message-ID: <4840D63F.2090407@redhat.com> Date: Fri, 30 May 2008 21:38:23 -0700 From: Ulrich Drepper Organization: Red Hat, Inc. User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Linus Torvalds CC: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mtk.manpages@gmail.com Subject: Re: [PATCH 0/3] 64-bit futexes: Intro References: <200805310127.m4V1RLR4013808@devserv.devel.redhat.com> <4840C29B.6030507@redhat.com> <4840CE51.9060109@redhat.com> In-Reply-To: X-Enigmail-Version: 0.95.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Linus Torvalds wrote: > Is it possible? I dunno. Once again not without limitations which are too low. The main problem is that there is far more information needed on the reader side. There are two counters and a number of bits for state information. Which means the counters can be at most 14 bits in size. A counter this low also means I cannot unconditionally increment them (since there can be more than 2^14 threads sharing one page). This means you get in the cache line race I described in the last mail. You first have to load a word and then perform a the write operation while at the same time other threads competing with you for the same cache line. > I personally suspect it is. I also suspect you > didn't even try. I have to disappoint you. I thought of that and had to reject it. - -- ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkhA1j8ACgkQ2ijCOnn/RHTUXQCgnkUy6PNSuUI4O6BD4abxqqKr PzMAn2qcvrXGM4qrhOytk1Yie0BsMeVa =zvxZ -----END PGP SIGNATURE-----