From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM power usage - high wakeup rates Date: Mon, 23 Jun 2008 05:51:05 +0300 Message-ID: <485F0F99.6060103@qumranet.com> References: <485AA6A7.2060806@codemonkey.ws> <485E59C3.1020607@flac.kalibalik.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Anders Return-path: Received: from il.qumranet.com ([212.179.150.194]:11398 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751531AbYFWCuy (ORCPT ); Sun, 22 Jun 2008 22:50:54 -0400 In-Reply-To: <485E59C3.1020607@flac.kalibalik.dk> Sender: kvm-owner@vger.kernel.org List-ID: Anders wrote: > Anthony Liguori wrote: >> With the default options, my idle winxp guest causes about 550 >> wakeups/sec which is pretty close to what I'd expect. I don't think >> you'll get much better than that without using a dynticks guest. > > According to powertop, I had about 15 kvm wakeups/sec with my previous > setup (nohz, no display). Now I upgraded to kvm-70 and the timer > interrupt has reappeared so I have this: > > Top causes for wakeups: > 25,4% (112,4) : function call interrupts > 22,6% (100,0) qemu-system-x86 : kvm_arch_vcpu_ioctl_run (pit_timer_fn) > 22,6% (100,0) qemu-system-x86 : __kvm_migrate_timers (apic_timer_fn) > 8,7% ( 38,5) qemu-system-x86 : sys_timer_settime (posix_timer_fn) > > What could be the cause for this change? The previous kvm was from > Ubuntu 8.04, there are no changes in the guest. > Likely, the in-kernel pit. Try -no-kvm-pit. > In general, what are the best host/guest settings for a low number of > wakeups? dyntick on both. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.