From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753332AbYHPWbp (ORCPT ); Sat, 16 Aug 2008 18:31:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751696AbYHPWbh (ORCPT ); Sat, 16 Aug 2008 18:31:37 -0400 Received: from casper.infradead.org ([85.118.1.10]:40818 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751282AbYHPWbg (ORCPT ); Sat, 16 Aug 2008 18:31:36 -0400 Date: Sat, 16 Aug 2008 15:31:09 -0700 From: Arjan van de Ven To: Jeremy Fitzhardinge Cc: Ingo Molnar , Jens Axboe , Peter Zijlstra , Christian Borntraeger , Linux Kernel Mailing List , Rusty Russell Subject: Re: [PATCH RFC 3/3] x86: use mwait for trigger API Message-ID: <20080816153109.3469878c@infradead.org> In-Reply-To: <48A74BAA.4010908@goop.org> References: <48A70192.7020002@goop.org> <20080816104404.070e0c14@infradead.org> <48A74BAA.4010908@goop.org> Organization: Intel X-Mailer: Claws Mail 3.5.0 (GTK+ 2.12.11; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 16 Aug 2008 14:50:34 -0700 Jeremy Fitzhardinge wrote: > Arjan van de Ven wrote: > > monitor/mwait is rather really expensive.. are we really sure we > > want to use this? > > (from an Intel cpu perspective the answer is very likely no; but I > > don't know what AMD does here) > > > > The intended use is when you're going to be waiting for a while (on > the order of microseconds or more). well mwait really is not cheap, I'd not be surprised if it's in that same order. > In the Xen case, I use this to > block the vcpu if we pass a few iterations without the condition > being true. While the mwait patch doesn't do this at present, it > could. that's another hard one.. passing C-state hints into mwait needs ACPI help; the BIOS tells us which mwait values are legal/valid at any point in time.. but this gets tricky to put into these spinpletions. -- If you want to reach me at my work email, use arjan@linux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org