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: Thu, 02 Dec 2010 21:21:25 -0600 Message-ID: <4CF86235.7050409@codemonkey.ws> References: <1291298357-5695-1-git-send-email-aliguori@us.ibm.com> <20101202191416.GQ10050@sequoia.sous-sol.org> <20101202204016.GB31316@amt.cnet> <20101202210737.GS10050@sequoia.sous-sol.org> <4CF81FC6.7090503@codemonkey.ws> <20101203024221.GX10050@sequoia.sous-sol.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm@vger.kernel.org, Avi Kivity , Srivatsa Vaddagiri To: Chris Wright Return-path: Received: from mail-gx0-f174.google.com ([209.85.161.174]:39432 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758350Ab0LCDV2 (ORCPT ); Thu, 2 Dec 2010 22:21:28 -0500 Received: by gxk1 with SMTP id 1so1600579gxk.19 for ; Thu, 02 Dec 2010 19:21:27 -0800 (PST) In-Reply-To: <20101203024221.GX10050@sequoia.sous-sol.org> Sender: kvm-owner@vger.kernel.org List-ID: On 12/02/2010 08:42 PM, Chris Wright wrote: > OK, let's say a single PCPU == 12 Compute Units. > > If the guest is the first to migrate to a newly added unused host, and > we are using either non-trapping hlt or Marcelo's non-yielding trapping > hlt, then that guest is going to get more CPU than it expected unless > there is some throttling mechanism. Specifically, it will get 12CU > instead of 1-3CU. > > Do you agree with that? > Yes. There's definitely a use-case to have a hard cap. But I think another common use-case is really just performance isolation. If over the course of a day, you go from 12CU, to 6CU, to 4CU, that might not be that bad of a thing. If the environment is designed correctly, of N nodes, N-1 will always be at capacity so it's really just a single node hat is under utilized. Regards, Anthony Liguori > thanks, > -chris >