[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] RE: rdtsc: correctness vs performance on Xen (and KVM?)
>>> Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> 01.09.09 17:26 >>> >> On 01/09/2009 15:53, "Dan Magenheimer" >> <dan.magenheimer@xxxxxxxxxx> wrote: >> >> > 1) fake rdmsr (or hypercall if it works) returns a virtual >> > address within a range of addresses that is not "owned by" >> > the OS (e.g. maybe in Xen address space?). The page is >> > only readable outside of ring 0, but writeable in ring 0 >> > (by Xen). >> > 2) All TLB misses on this page are handled directly by Xen >> > so the OS never sees the address/page. >> >> 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 can be made work - you just need to properly arrange this and the compatibility p2m table. >> > If these are OK, and you see other parts of the proposal >> > that require PV kernel mods, please point them out. >> >> 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 within today's Xen or Linux (which both assume a global kernel address space, in particular non-root page table entries mapping kernel space to be the same in all address spaces - you'd need separate entries at all levels for this). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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