From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262655AbTLNVP5 (ORCPT ); Sun, 14 Dec 2003 16:15:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262679AbTLNVP5 (ORCPT ); Sun, 14 Dec 2003 16:15:57 -0500 Received: from qlink.QueensU.CA ([130.15.126.18]:12451 "EHLO qlink.queensu.ca") by vger.kernel.org with ESMTP id S262655AbTLNVPv (ORCPT ); Sun, 14 Dec 2003 16:15:51 -0500 Subject: Re: HT schedulers' performance on single HT processor From: Nathan Fredrickson <8nrf@qlink.queensu.ca> To: Adam Kropelin Cc: Con Kolivas , Linux Kernel Mailing List , Nick Piggin , Ingo Molnar , sam@mars.ravnborg.org In-Reply-To: <20031214153504.A6795@mail.kroptech.com> References: <200312130157.36843.kernel@kolivas.org> <1071431363.19011.64.camel@rocky> <20031214153504.A6795@mail.kroptech.com> Content-Type: text/plain Message-Id: <1071436539.19124.6.camel@rocky> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.5 (1.4.5-7) Date: Sun, 14 Dec 2003 16:15:40 -0500 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2003-12-14 at 15:35, Adam Kropelin wrote: > On Sun, Dec 14, 2003 at 02:49:24PM -0500, Nathan Fredrickson wrote: > > Same table as above normalized to the j=1 uniproc case to make > > comparisons easier. Lower is still better. > > > > j = 1 2 3 4 8 > > 1phys (uniproc) 1.00 1.00 1.00 1.00 1.00 > > 1phys w/HT 1.02 1.02 0.87 0.87 0.87 > > 1phys w/HT (w26) 1.02 1.02 0.87 0.87 0.88 > > 1phys w/HT (C1) 1.03 1.02 0.88 0.88 0.88 > > 2phys 1.00 1.00 0.53 0.53 0.53 > ^^^^^ ^^^^ > > Ummm... > > This is mighty suspicious. With -j2 did you check to see that there > were indeed two parallel gcc's running? Since -test6 I've found that > -j2 only results in a single gcc instance. I've seen this on both an > old hacked-up RH 7.3 installation and a brand new RH 9 + updates > installation. I just checked and you're right, the number of compilers that actually run is j-1, for all j>1. I assume this is a problem with the parallel build process, but it does not invalidate these results for comparing the scheduler performance with different patches. > > > This suggests that j should be set to at least the number of logical > > processors + 1. > > Since -test6 I've found this to be the case for kernel builds, yes. But > I don't think it has anything to do with the scheduler or HT vs SMP > platforms. The 1-3% performance loss when HT is enabled for -j1 is still very real. Nathan