On Mon, 2008-03-24 at 00:32 +0900, Ryota OZAKI wrote: > Hi Avi, > > > If you use the dyntick clock option (the default, IIRC), and a newer > > host kernel, then the kernel provides high-resolution timers, very > > likely using HPET internally or some other high resolution clock and > > event source. > > I see. The dyntick clock seems to be more scalable than > the others. I understood that '-clock hpet' is used for > boosting one VM (becuase hpet gains best performance > on virtio), right? > > I would like to try dyntick for my multiple VMs environment. > > > I think that for newer kernels we already have the desired accuracy. > > Yes. In recent versions of kvm, I didn't experience > any time inaccuracy, although I had only tested under > several VMs. I'll try the more number of VMs, and > if time inaccuracy occurs, I would like to report > that. >
The problem is not inaccuracy of guest clock (which we do suffer from in some guests and there is work in progress to fix). The problem is that qemu_timer is not accurate, thus the virtio tx timer is too slow leading to not optimized performance for virtio-net. Try host kernel >= 2.6.24 with dyntick. > Many thanks, > ozaki-r > > 2008/3/23, Avi Kivity <[EMAIL PROTECTED]>: > > Ryota OZAKI wrote: > > > Hi all, > > > > > > Current kvm allows only one VM to use HPET. Is > > > there a plan to implement a functionality to > > > allow multiple VMs to use HPET? If so, how > > > about the status of that? > > > > > > > > > > > > If you use the dyntick clock option (the default, IIRC), and a newer > > host kernel, then the kernel provides high-resolution timers, very > > likely using HPET internally or some other high resolution clock and > > event source. > > > > > > > And I would like to ask right and wrong to > > > implement the functionality in terms of need > > > and efficiency (scalability and time accuracy). > > > > > > I think that for newer kernels we already have the desired accuracy. > > We're not always good at exploiting that accuracy; hence the recent > > movement of the PIT implementation from userspace to the kernel. But > > recent discussion leads me to believe it could have been implemented > > with the userspace PIT as well. > > > > > > -- > > Any sufficiently difficult bug is indistinguishable from a feature. > > > > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2008. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > kvm-devel mailing list > kvm-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/kvm-devel ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
