From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932454AbXHNDZo (ORCPT ); Mon, 13 Aug 2007 23:25:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758243AbXHNDZ3 (ORCPT ); Mon, 13 Aug 2007 23:25:29 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:60193 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752994AbXHNDZ2 (ORCPT ); Mon, 13 Aug 2007 23:25:28 -0400 Date: Mon, 13 Aug 2007 20:25:28 -0700 (PDT) Message-Id: <20070813.202528.05603304.davem@davemloft.net> To: akpm@linux-foundation.org Cc: jens.axboe@oracle.com, npiggin@suse.de, mingo@elte.hu, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: lmbench ctxsw regression with CFS From: David Miller In-Reply-To: <20070813200038.7fc8a9e6.akpm@linux-foundation.org> References: <20070806032949.GA16401@wotan.suse.de> <20070813123031.GS23758@kernel.dk> <20070813200038.7fc8a9e6.akpm@linux-foundation.org> X-Mailer: Mew version 5.1.52 on Emacs 21.4 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Andrew Morton Date: Mon, 13 Aug 2007 20:00:38 -0700 > Guys, repeat after me: "context switch is not a fast path". Take > that benchmark and set fire to it. Nothing in this world is so absolute :-) Regardless of the value of lat_ctx, we should thank it for showing that something is more expensive now. And it definitely warrants figuring out what paths are big cycle eaters now and why. Not "on IA64 indirect calls are expensive, so that must be it", but rather doing cycle analysis of the relevant scheduling functions to figure out what might be wrong. I'm willing to bet it's something completely trivial and easy to amend, rather than a fundamental issue. But somebody has to _look_ instead of supposing this and that.