From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: kvm & dyntick Date: Fri, 12 Jan 2007 19:04:31 +0200 Message-ID: <45A7BF9F.5090508@qumranet.com> References: <45A66106.5030608@qumranet.com> <20070112062006.GA32714@elte.hu> <20070112101931.GA11635@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel , linux-kernel Return-path: To: Ingo Molnar In-Reply-To: <20070112101931.GA11635-X9Un+BFzKDI@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 Ingo Molnar wrote: > * Ingo Molnar wrote: > > >>> 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) >> > > using the dynticks code from the -rt kernel makes the overhead of an > idle guest go down by a factor of 10-15: > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 2556 mingo 15 0 598m 159m 157m R 1.5 8.0 0:26.20 qemu > > As usual, great news. > ( for this to work on my system i have added a 'hyper' clocksource > hypercall API for KVM guests to use - this is needed instead of the > running-to-slowly TSC. ) > What's the problem with the TSC? The only issue I'm aware of is that the tsc might go backwards if the vcpu is migrated to another host cpu (easily fixed). A pv clocksource makes sense in any case. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- 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