On 2012-01-20 11:14, Marcelo Tosatti wrote: > On Thu, Jan 19, 2012 at 07:01:44PM +0100, Jan Kiszka wrote: >> On 2012-01-19 18:53, Marcelo Tosatti wrote: >>>> What problems does it cause, and in which scenarios? Can't they be >>>> fixed? >>> >>> If the guest compensates for lost ticks, and KVM reinjects them, guest >>> time advances faster then it should, to the extent where NTP fails to >>> correct it. This is the case with RHEL4. >>> >>> But for example v2.4 kernel (or Windows with non-acpi HAL) do not >>> compensate. In that case you want KVM to reinject. >>> >>> I don't know of any other way to fix this. >> >> OK, i see. The old unsolved problem of guessing what is being executed. >> >> Then the next question is how and where to control this. Conceptually, >> there should rather be a global switch say "compensate for lost ticks of >> periodic timers: yes/no" - instead of a per-timer knob. Didn't we >> discussed something like this before? > > I don't see the advantage of a global control versus per device > control (in fact it lowers flexibility).
Usability. Users should not have to care about individual tick-based clocks. They care about "my OS requires lost ticks compensation, yes or no". Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
