On 10/12/07, Hollis Blanchard <[EMAIL PROTECTED]> wrote: > > 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). > > As I understand it, the TSC is based on CPU frequency, which changes > with power management. Architectural bug. No. The TSC _used_ to be tied to CPU frequency. Current architectural trends keep it constant, and provides other methods for cycle counting. So in newer machines, the tsc should be constant.
> However, PV time still doesn't help here: > * The TSC is _user_ accessible, so PV time support in the guest > kernel doesn't solve the problem. I'm not sure about which (of them) problem you are talking about here. > * It looks like external agents can perform out-of-kernel > frequency scaling on x86 (at least I see options for it on IBM > blades). So there must already exist some mechanism for a kernel > to be informed that the TSC frequency has been changed. If the TSC frequency can be changed, I don't use tsc as a ultimate resort of timing at all, but rather, just for micro-adjustments. > > 3) a PV clock can support stolen time calculation which there really > > isn't a concept of with emulation. > > This is true, and I know other platforms support this functionality. I > think it's mostly useful for process time accounting. Is that actually > supported in this patch? > > -- > Hollis Blanchard > IBM Linux Technology Center > > -- Glauber de Oliveira Costa. "Free as in Freedom" http://glommer.net "The less confident you are, the more serious you have to act." ------------------------------------------------------------------------- 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
