2008/3/24, Dor Laor <[EMAIL PROTECTED]>: > > 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.
My apology. As you pointed out, I confused them. > Try host kernel >= 2.6.24 with dyntick. I tried 2.6.25-rc5 with dyntick, but in my evaluation, the tx performance of virtio-net achieves only a half of rx performance; tx is 446 Mbps whereas rx is 913 Mbps. Is this best tx performance at this time, or not? (If that helps, tx with HPET achieves 524 Mbps.) My experimental setup is: host cpu: Xeon E5410 2.33 GHz (Quad cores) x 2 host kenrel: linux-2.6.25-rc5 kvm: kvm-63 guest kernel: 'rusty' branch in dor's git (commit 3fdd01dfef3ab175f7aaf499dd6759205028692c) tool: iperf ozaki-r > > > 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
