From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [PATCH/RFC] report hardware tsc frequency even for emulated tsc Date: Mon, 30 Nov 2009 13:06:44 -0800 Message-ID: <4B1433E4.5070604@goop.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Dan Magenheimer Cc: "Xen-Devel (E-mail)" , Keir Fraser List-Id: xen-devel@lists.xenproject.org On 11/30/09 12:51, Dan Magenheimer wrote: > As long as the "illusion" provided via both rdtsc and > pvclock are consistent, it works. > OK, I see. Rather than always emulating 1GHz, make it emulate some other arbitrary speed depending on the initial native CPU speed. > I wasn't aware of that. My proposal could allow for that but > the specific proposed patch doesn't. It could only be > done I think if one didn't care about the TSC hz rate > given to apps... if that's true, just turn off TSC emulation. > I don't think its worth doing. In many ways a VCPU is like a Transmeta CPU: they never ran at any particular speed, but with some power/performance policy setting. The tsc ran at a fixed rate that had no particular relationship to how fast instructions get executed. > Good point. OTOH, if one cared to do something to change > tsc emulation, one would need to be privileged to relaunch > the domain. > Well, they'd need some interface to start domains at all. You could imagine something like a VPS hosting service where the user can control their own domains via a web GUI, and "tsc emulation" would be a checkbox (buried deeping in an advanced options page, one presumes). And you could also imagine that this patch would be a boon to them, because it would eliminate the "you said you had 2.4GHz hosts but /proc/cpuinfo only says 1GHz" questions/complaints... J