On Sun, Sep 26, 2010 at 12:36:54PM +0200, Avi Kivity wrote: > On 09/24/2010 04:49 AM, Julien Desfossez wrote: > >Hello, > > > >I'd like to access the host TSC from the inside of a guest kernel > >and I don't really know if it's possible. > > > >I'm working with kvm_clock and I have been playing with the > >pvclock_vcpu_time_info structure, but I'm not sure if I'm in the > >right direction. > > > >So could you tell me if there is an efficient way to access to > >access the host TSC (or at least the TSC_OFFSET) from a module > >inside a guest kernel ? > > > >I did it with an hypercall, but it's for tracing purpose and doing > >an hypercall every time I want to record an event, is way too > >costly. > > It isn't possible. If you need a coherent host/guest timestamp, I > suggest using ktime_get(). I think Avi meant that it isn't possible with stock KVM. If you hack KVM to run the guest with 'RDTSC exiting' set to 0 and either disable 'use TSC offseting' or communicate the TSC offset to the guest out of band, you should have efficient & consistent guest/host timestamps. Cheers, Muli -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
