From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754633AbYIFSab (ORCPT ); Sat, 6 Sep 2008 14:30:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752372AbYIFSaX (ORCPT ); Sat, 6 Sep 2008 14:30:23 -0400 Received: from yx-out-2324.google.com ([74.125.44.29]:13496 "EHLO yx-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752164AbYIFSaX (ORCPT ); Sat, 6 Sep 2008 14:30:23 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=LJEnhZZqVynkMCs7rjjiYAPwgErKgnOf3Bb8ojLp7Y2dVIUue7vBfh8SorOr8RBdMq mgyeN3c0n52PwCueYokcVM/hHJ6BTGO7fBWUREGeGtMVqvy+7tOF4Z4KNNibfs9l7C4N yXP0iNvURO+0GDb6xWIJjwaNDN1nd5rWWd7DE= Message-ID: Date: Sat, 6 Sep 2008 11:30:21 -0700 From: "Ulrich Drepper" To: "Arjan van de Ven" Subject: Re: nice and hyperthreading on atom Cc: "Phil Endecott" , "Linux Kernel Mailing List" In-Reply-To: <20080906094248.5930911a@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1220715811849@dmwebmail.dmwebmail.chezphil.org> <20080906094248.5930911a@infradead.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Sep 6, 2008 at 9:42 AM, Arjan van de Ven wrote: > As an OS one COULD decide to just not schedule the nice task at all, > but then, especially on atom where HT has a high efficiency, your cpu > is mostly idle ... One thread being idle is even on Atom the right thing to do in some situations. If you have processes which, when HT is used, experience high pressure on the common cache(s) then you should not schedule them together. We can theoretically find out whether this is the case using the PMCs. With perfmon2 hopefully on the horizon soon it might actually be possible to automatically make these measurements. There is another aspect I talked to Peter about already. We really want concurrent threat scheduling in some cases. For the implementation of helper threads you don't want two threads to be scheduled independently, you want them to be scheduled on a HT pair. Currently this isn't possible except by pinning them to fixed threads. We really want to have a new way to express this type of scheduling (Peter, how did you call it?)