Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755882AbYHMPle (ORCPT ); Wed, 13 Aug 2008 11:41:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753902AbYHMPlS (ORCPT ); Wed, 13 Aug 2008 11:41:18 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:52281 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753736AbYHMPlR (ORCPT ); Wed, 13 Aug 2008 11:41:17 -0400 Date: Wed, 13 Aug 2008 17:40:43 +0200 From: Ingo Molnar To: Ulrich Drepper Cc: Arjan van de Ven , akpm@linux-foundation.org, hugh@veritas.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, briangrant@google.com, cgd@google.com, mbligh@google.com, Linus Torvalds , Thomas Gleixner , "H. Peter Anvin" Subject: Re: pthread_create() slow for many threads; also time to revisit 64b context switch optimization? Message-ID: <20080813154043.GA11886@elte.hu> References: <20080813104445.GA24632@elte.hu> <20080813063533.444c650d@infradead.org> <48A2EE07.3040003@redhat.com> <20080813142529.GB21129@elte.hu> <48A2F157.7000303@redhat.com> <20080813151007.GA8780@elte.hu> <48A2FC17.9070302@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <48A2FC17.9070302@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1883 Lines: 43 * Ulrich Drepper wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Ingo Molnar wrote: > > i find it pretty unacceptable these days that we limit any aspect of > > pure 64-bit apps in any way to 4GB (or any other 32-bit-ish limit). > > Sure, but if we can pin-point the sub-archs for which it is the > problem then a flag to optionally request it is even easier to handle. > You'd simply ignore the flag for anything but the P4 architecture. i suspect you are talking about option #2 i described. It is the option which will take the most time to trickle down to people. > I personally have no problem removing the whole thing because I have > no such machine running anymore. But there are people out there who > have. hm, i think the set of people running on such boxes _and_ then upgrading to a new glibc and expecting everything to be just as fast to the microsecond as before should be miniscule. Those P4 derived 64-bit boxes were astonishingly painful in 64-bit mode - most of that hw is running 32-bit i suspect, because 64-bit on it was really a joke. Btw., can you see any problems with option #1: simply removing MAP_32BIT from 64-bit stack allocations in glibc unconditionally? It's the fastest to execute and also the most obvious solution. +1 usecs overhead in the 64-bit context-switch path on those old slow boxes wont matter much. 10 _millisecs_ to start a single thread on top-of-the-line hw is quite unaccepable. (and there's little sane we can do in the kernel about allocation overhead when we have an imperfectly filled 4GB box for all allocations) Ingo -- 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/