[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Xen hiding thermal capabilities from Dom0
On Thu, Nov 21, 2019 at 07:09:31PM +0530, Rishi wrote: > On Tue, Nov 19, 2019 at 2:47 PM Jan Beulich <jbeulich@xxxxxxxx> wrote: > > > > On 19.11.2019 06:23, Rishi wrote: > > > ok, thanks for clearing it up. Would a patch be accepted if this > > > option of showing EAX leaf is selectively done through command line > > > (default disabled)? > > > > In general I'd expect this to be rather unlikely, but I guess much > > would depend on the actual reasoning done in the description. > > > > > On longer run, what is an expected sane model of virtualizing this? > > > With some guidance, may be I or someone else can code to bring the > > > functionality back. > > > > Which functionality? So far you've talked of only CPUID bits I > > think, without explaining at all what functionality you want to > > have that depends on these. In general, as said earlier, CPU > > management is the hypervisor's responsibility, so I'd rather > > not see this virtualized, but the hypervisor be put into a > > position of doing whatever is needed. > > > > Jan > > The reasoning to have EAX(0x06h) exposed to Dom0 is for Thermal and > Power management. > Without EAX(0x06h) Dom0 is unable to sense presence of CPU core > temperature or do Thermal management - including but not limited to > operating Fan speed. > Dom0 has to rely on other possible ways such as ipmi or BIOS which are > optionally available. > > From the patch description > https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=72e038450d3d5de1a39f0cfa2d2b0f9b3d43c6c6 > it seems that the change was introduced to not expose EAX(0x06h) to > unprivileged PV guests but nothing is said for Dom0 itself. I think > you already mentioned that the flag is hid from Dom0 as well > intentionally. > > So unless hypervisor wants to do thermal management of the CPU board, > it would inhibit Dom0's ability to do this function. That's likely what you want, on a Xen system dom0 is a special guest, but still a guest, so it's not feasible for a native dom0 driver to do power or temperature management without having Xen specific knowledge. For instance the load on dom0 doesn't match the actual load on the hardware. I think we had a very similar discussion at: https://marc.info/?l=xen-devel&m=156397696413230&w=2 I would recommend reading the full thread and the conclusions/proposals. Roger. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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