On Tue, 2007-03-06 at 16:42 -0800, Dan Hecht wrote: > >> accounting would be wrong. Instead, we should allow the > >> tick_sched_timer in cases (c) and (d) to have runtime configurable > >> period, and then scale the time value accordingly before passing to > >> account_system_time. This is probably something the Xen folks will want > >> also, since I think Xen itself only gets 100hz hard timer, and so it can > >> implement at best a oneshot virtual timer with 100hz resolution. Any > >> objections to us doing something like this? > > > > Yes. It's gross hackery. > > > > 1) We want to have a cleanup of the tick assumptions _all_ over the > > place and this is going to be real hard work. > > > > 2) As I said above. The time accounting for virtualization needs to be > > fixed in a generic way. > > > > I'm not going to accept some weird hackery for virtualization, which is > > of exactly ZERO value for the kernel itself. Quite the contrary it will > > make the cleanup harder and introduce another hard to remove thing, > > which will in the worst case last for ever. > > > > Okay, to confirm I'm on the same page as you, you want to move process > time accounting from being periodic sampled based to being trace based? > i.e. at the system-call/interrupt boundaries, read clocksource and > compute directly the amount of system/user/process time? At least for the paravirt guests this is the correct approach. Once the CPU vendors come up with a sane solution for a reliable and fast clock source we might use that on real hardware as well. > Do you know if anyone has explored this? I thought there was a > discussion about this a while back but it was rejected due to the > sample-based approach having much lower overheads on high system call > rate workloads. Yes, with todays hardware it is simply a PITA. PowerPC has some basic support for this though, IIRC. tglx _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxx https://lists.osdl.org/mailman/listinfo/virtualization
