I was planning on diving into Xen with the release of Fedora core 6 and the improved Xen support it has, but one thing surprised me: My dual core amd64 system runs more than five degrees hotter when idle than the non-Xen kernel runs on the same box. Is this normal? Is the hypervisor missing interfaces to let dom0 do the energy-star magic for it? Is anyone even worried about this? Or is it all just a bug with Fedora''s kernel? Just curious at this point, but it does seem like it might be an important issue. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
> -----Original Message----- > From: xen-devel-bounces@lists.xensource.com > [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of > Tom Horsley > Sent: 30 October 2006 14:35 > To: xen-devel@lists.xensource.com > Subject: [Xen-devel] Xen not very green? > > I was planning on diving into Xen with the release of Fedora > core 6 and the improved Xen support it has, but one thing > surprised me: My dual core amd64 system runs more than > five degrees hotter when idle than the non-Xen kernel > runs on the same box.Is your non-Xen kernel running power-management (cpufreq and friends)? It is possible to do that on Xen also, but it''s not compiled in as standard, and I don''t remember if the patch for it is applied to Xen or you have to get the patch from somewhere... [Although if you run more than Dom0 on the system, severeal potential problems crop up, the most immediate one is that Dom0''s CPU usages becomes the deciding factor for the entire system, and the DomU''s cpu speed will not be updated by the changes in the Dom0!] Of course, there are some other factors that may also affect the power consumption of the processor: 1. There is more code to run in Xen - even in "idle". 2. All of the interrupt handling, task switching, page-table management and such is more complex with Xen than with the stock linux kernel - all of which affects even the system when idle, since even an idle system will do some sorts of "housekeeping behind the scenes" that you don''t necessarily see in the overall performance of the system, but does happen still. This is of course just theories, I haven''t actually studied the exact behaviour of the CPU in the two cases... -- Mats> > Is this normal? > > Is the hypervisor missing interfaces to let dom0 > do the energy-star magic for it? > > Is anyone even worried about this? > > Or is it all just a bug with Fedora''s kernel? > > Just curious at this point, but it does seem like > it might be an important issue. > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
I think power management is a little less developed in Xen than in Linux so it''s not going to be able to utilise the low power states in your hardware quite as well for the moment. It''s something that''s up for improvement - particularly as folks like to run Xen on laptops some times. Worth noting though, that if you are aggregating lots of servers onto one Xen box instead of on multiple physical boxes you are quite possibly going to save power over all, in which case Xen would be greener. HTH, Mark On Monday 30 October 2006 14:34, Tom Horsley wrote:> I was planning on diving into Xen with the release of Fedora > core 6 and the improved Xen support it has, but one thing > surprised me: My dual core amd64 system runs more than > five degrees hotter when idle than the non-Xen kernel > runs on the same box. > > Is this normal? > > Is the hypervisor missing interfaces to let dom0 > do the energy-star magic for it? > > Is anyone even worried about this? > > Or is it all just a bug with Fedora''s kernel? > > Just curious at this point, but it does seem like > it might be an important issue. > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel-- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
On 30/10/06 18:13, "Mark Williamson" <mark.williamson@cl.cam.ac.uk> wrote:> I think power management is a little less developed in Xen than in Linux so > it''s not going to be able to utilise the low power states in your hardware > quite as well for the moment. > > It''s something that''s up for improvement - particularly as folks like to run > Xen on laptops some times. > > Worth noting though, that if you are aggregating lots of servers onto one Xen > box instead of on multiple physical boxes you are quite possibly going to > save power over all, in which case Xen would be greener.I think Rik van Riel might be doing some investigation. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel