From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v2) Date: Fri, 03 Dec 2010 12:07:15 -0600 Message-ID: <4CF931D3.6000204@codemonkey.ws> References: <1291298357-5695-1-git-send-email-aliguori@us.ibm.com> <20101202191416.GQ10050@sequoia.sous-sol.org> <20101203115752.GD27994@linux.vnet.ibm.com> <20101203162731.GA11725@linux.vnet.ibm.com> <20101203172906.GD10050@sequoia.sous-sol.org> <20101203175744.GE13515@linux.vnet.ibm.com> <20101203175854.GF10050@sequoia.sous-sol.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Srivatsa Vaddagiri , Anthony Liguori , kvm@vger.kernel.org, Avi Kivity , Marcelo Tosatti To: Chris Wright Return-path: Received: from mail-gw0-f46.google.com ([74.125.83.46]:45907 "EHLO mail-gw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752702Ab0LCSHS (ORCPT ); Fri, 3 Dec 2010 13:07:18 -0500 Received: by gwj20 with SMTP id 20so4942987gwj.19 for ; Fri, 03 Dec 2010 10:07:17 -0800 (PST) In-Reply-To: <20101203175854.GF10050@sequoia.sous-sol.org> Sender: kvm-owner@vger.kernel.org List-ID: On 12/03/2010 11:58 AM, Chris Wright wrote: > * Srivatsa Vaddagiri (vatsa@linux.vnet.ibm.com) wrote: > >> On Fri, Dec 03, 2010 at 09:29:06AM -0800, Chris Wright wrote: >> >>> That's what Marcelo's suggestion does w/out a fill thread. >>> >> There's one complication though even with that. How do we compute the >> real utilization of VM (given that it will appear to be burning 100% cycles)? >> We need to have scheduler discount the cycles burnt post halt-exit, so more >> stuff is needed than those simple 3-4 lines! >> > Heh, was just about to say the same thing ;) > My first reaction is that it's not terribly important to account the non-idle time in the guest because of the use-case for this model. Eventually, it might be nice to have idle time accounting but I don't see it as a critical feature here. Non-idle time simply isn't as meaningful here as it normally would be. If you have 10 VMs in a normal environment and saw that you had only 50% CPU utilization, you might be inclined to add more VMs. But if you're offering deterministic execution, it doesn't matter if you only have "50%" utilization. If you add another VM, the guests will get exactly the same impact as if they were using 100% utilization. Regards, Anthony Liguori > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >