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[Xen-devel] Re: rdtsc: correctness vs performance on Xen (and KVM?)
| To: | Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
|---|---|
| Subject: | [Xen-devel] Re: rdtsc: correctness vs performance on Xen (and KVM?) |
| From: | Keir Fraser <keir.fraser@xxxxxxxxxxxxx> |
| Date: | Tue, 01 Sep 2009 16:43:52 +0100 |
| Cc: | "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> |
| Delivery-date: | Tue, 01 Sep 2009 08:44:30 -0700 |
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| Thread-index: | AcorGJhXOrlW5pSyS7KJ8GUcPXtzrwAAmj85 |
| Thread-topic: | rdtsc: correctness vs performance on Xen (and KVM?) |
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On 01/09/2009 16:26, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote: >> I think these are probably possible, at least for a 64-bit >> hypervisor which >> isn't playing segment limit tricks. > > Will it work for pv32_on_64? (I don't care much about > 32-bit hypervisor.) It could do. Space is reserved at the top of 4GB for the M2P tables, and I suppose such a mapping could go there. >> Won't the pvclock computation be per-cpu? How will you deal with >> that? > > Hmmm... is it possible for the same virtual address/page > to map to a different physical address/page on each processor? Not without PV guest kernel support. The guest kernel manages the page directories. And Linux runs threads on exactly the same pagetables across different cpus. That would have to change. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel |
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