From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: idle linux guest takes up to 8.5% of host CPU Date: Sun, 22 Jul 2007 17:54:20 +0300 Message-ID: <46A36F9C.3030809@qumranet.com> References: <9ebd65110707220739j761ada89wec0eb8194b63e8d0@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Adam Monsen Return-path: In-Reply-To: <9ebd65110707220739j761ada89wec0eb8194b63e8d0-JsoAwUIsXosN+BqQ9rBEUg@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 Adam Monsen wrote: > I have a Fedora 7 host with two guests: > lnx01: Fedora 7 > win01: Windows XP Pro > > When they are both active, the host CPU usage by the Linux guest > hovers around 8 to 9 percent, while the host CPU usage by the Windows > guest hovers around 1 to 1.5 percent. These values are seen in the > "virt-manager" application. > > Any idea why an idle Fedora 7 guest would use more host CPU than an > idle Windows XP guest? > > Several reasons: - Linux userspace sucks up more cpu than Windows. That's especially true if you have X running. - If running a 64-bit kernel, Linux is running at 250Hz or 300Hz whereas Windows runs at 100Hz unless you're doing multimedia. F7 32-bit kernels adjust the timer dynamically. - If your machine is idle, it scales down the clock frequency, making guest idle usage seem higher (that doesn't account for the difference between Linux and Windows, though). That said, I usually see much lower numbers. Maybe you have an older cpu. Also do look at http://kvm.qumranet.com/kvmwiki/Windows_ACPI_Workaround for possibly reducing Windows cpu usage further. When the apic work is merged, I expect idle cpu usage to drop dramatically. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/