From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: kvm & dyntick Date: Fri, 12 Jan 2007 07:20:07 +0100 Message-ID: <20070112062006.GA32714@elte.hu> References: <45A66106.5030608@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel , linux-kernel Return-path: To: Avi Kivity Content-Disposition: inline In-Reply-To: <45A66106.5030608-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.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 ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV