Hollis Blanchard wrote: > On Fri, 2007-10-12 at 13:08 -0300, Glauber de Oliveira Costa wrote: > >> +config KVM_CLOCK >> + bool "KVM paravirtualized clock" >> + depends on PARAVIRT && GENERIC_CLOCKEVENTS >> + help >> + Turning on this option will allow you to run a paravirtualized >> clock >> + when running over the KVM hypervisor. Instead of relying on a PIT >> + (or probably other) emulation by the underlying device model, the >> host >> + provides the guest with timing infrastructure, as time of day, and >> + timer expiration. >> > > I must have missed earlier discussion on this topic, so I'm left > wondering... what's the point? What's wrong with PIT (et al) emulation? >
There are three separate reasons, that I know of, to have a PV timer. 1) the PIT is periodic. a PV timer can offer a one shot timer which enables dynticks. 2) the TSC would have to be used as a clocksource. You don't know the frequency which is the first problem with using the TSC but some systems have a TSC that changes frequencies. A PV time source gives you more stable clocksource (although as in glommer's patch, when the TSC can be used, it's better to use it). 3) a PV clock can support stolen time calculation which there really isn't a concept of with emulation. Regards, Anthony Liguori ------------------------------------------------------------------------- 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
