Dan Hecht wrote: > Not really. In the case hardware TSC is perfect, the paravirt time > counter can be implemented directly in terms of hardware TSC; there is > no loss in optimization. This is done transparently. And virtual TSC > can be implemented this way too. > > The real improvement that a paravirt clocksource offers over the TSC > clocksource is that the guest does not need to measure the TSC frequency > itself against some other constant frequency source (which is > problematic on a virtual machine). Instead, the paravirt clocksource > queries the hypervisor for the frequency of the counter. As you know, > with clocksource style kernels, it's important to get this frequency > correct, or else the guest will have long-term time drift. > >
In addition, a paravirt clocksource can compensate for events like vcpu migration to another host cpu. So I agree: a paravirt clocksource is always better than or equal to the tsc. -- Any sufficiently difficult bug is indistinguishable from a feature. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
