From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1160995AbXALGYi (ORCPT ); Fri, 12 Jan 2007 01:24:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161005AbXALGYh (ORCPT ); Fri, 12 Jan 2007 01:24:37 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:41727 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1160995AbXALGYg (ORCPT ); Fri, 12 Jan 2007 01:24:36 -0500 Date: Fri, 12 Jan 2007 07:20:07 +0100 From: Ingo Molnar To: Avi Kivity Cc: kvm-devel , linux-kernel , Thomas Gleixner Subject: Re: kvm & dyntick Message-ID: <20070112062006.GA32714@elte.hu> References: <45A66106.5030608@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45A66106.5030608@qumranet.com> User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -5.9 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-5.9 required=5.9 tests=ALL_TRUSTED,BAYES_00 autolearn=no SpamAssassin version=3.0.3 -3.3 ALL_TRUSTED Did not pass through any untrusted hosts -2.6 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Avi Kivity wrote: > It occurs to me that kvm could benefit greatly from dyntick: > > dyntick-enabled host: > - generate virtual interrupts at whatever HZ the guest programs its > timers, be it 100, 250, 1000 or whatever > - avoid expensive vmexits due to useless timer interrupts > > dyntick-enabled guest: > - reduce the load on the host when the guest is idling > (currently an idle guest consumes a few percent cpu) yeah. KVM under -rt already works with dynticks enabled on both the host and the guest. (but it's more optimal to use a dedicated hypercall to set the next guest-interrupt) > What are the current plans wrt dyntick? Is it planned for 2.6.21? yeah, we hope to have it in v2.6.21. note that s390 (and more recently Xen too) uses a next_timer_interrupt() based method to stop the guest tick - which works in terms of reducing guest load, but it doesnt stop the host-side interrupt. The highest quality approach is to have dynticks on both the host and the guest, and this also gives high-resolution timers and a modernized time/timer-events subsystem for both the host and the guest. Ingo