Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754955Ab3JCS2v (ORCPT ); Thu, 3 Oct 2013 14:28:51 -0400 Received: from mail.skyhub.de ([78.46.96.112]:49705 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754929Ab3JCS2t (ORCPT ); Thu, 3 Oct 2013 14:28:49 -0400 Date: Thu, 3 Oct 2013 20:28:45 +0200 From: Borislav Petkov To: Austin S Hemmelgarn Cc: Linus Torvalds , Linux-Kernel mailing list , Alan Cox Subject: Re: [PATCH 1/1] x86_64: add config options to optimize for newer AMD processors Message-ID: <20131003182845.GB17417@pd.tnic> References: <52486938.4090009@gmail.com> <20130929180101.GB5490@pd.tnic> <5248905E.8000801@gmail.com> <20130929205051.GD5426@pd.tnic> <52489A59.7040108@gmail.com> <20130929213026.GF5426@pd.tnic> <524D5DAC.3000004@gmail.com> <20131003165740.GA17417@pd.tnic> <524DB377.2070909@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <524DB377.2070909@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2005 Lines: 56 On Thu, Oct 03, 2013 at 02:12:07PM -0400, Austin S Hemmelgarn wrote: > Part of the difference between our results may be that I have my > entire userspace built with -mtune=bdver2, so less of the time is > spent in userspace. That still cannot explain the huge difference between building on a mk8 vs bdver2 kernel. Provided your userspace is the same and only the kernels are different, I don't see how that happens. Btw, you could run my workload on your machine, once on an mk8 kernel and once on a bdver2 one. The contents of the pre-build-kernel.sh script are: -- #!/bin/bash make -s clean echo 3 > /proc/sys/vm/drop_caches -- Of course, you need to run this as root. > Also, the part about using many more threads than cpu cores was with > regards to sysbench, not the kernel build, for that I just used 8 jobs > in make. Overcommitting gcc threads does not bring a really a big difference with a kernel build. > With regards to the differences shown above relative to CONFIG_MK8, > that does actually make sense; with CONFIG_MK8, gcc makes very minimal > use of extension instructions (afaik, only MMX, SSE, and 3Dnow!), this > improves performance slightly on bulldozer derivatives because there > are only half as many SSE and FP units as CPU cores (and the yes, the FPU is shared between the cores of a compute unit on BD. > scheduler isn't as smart as it could be with regards to that, but that > is something for another patch as far as I am concerned). Again, with unchanging userspace and only differing kernels, you shouldn't be seeing such a big difference. Besides, the kernel itself makes very little, if at all, use of FPU instructions. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. -- -- 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/