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xen-devel
[Xen-devel] Re: rdtsc hypercall, from userland?!? (was: rdtsc: correctne
>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 09.09.09 20:59 >>>
>You could enable/disable emulation rdtsc each context switch according
>to the app's desires/requrements. It would require an extra hypercall
>per context switch, but it could be batched with the others, resulting
>in little marginal cost. It would, however, leave the kernel's use of
>rdtsc in a confused state.
Not necessarily: There could be two flags, one saying app rdtsc needs to
be emulated, and a second one for the kernel ones'. Unless a pv kernel
wants this, its (emulated) reads could still return the real (hardware)
value rather than the calculated, 1GHz-based one.
Jan
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