On Mon, Oct 02, 2017 at 10:12:49AM -0700, Jacob Pan wrote: > On Sat, 30 Sep 2017 01:21:43 +0200 > "Rafael J. Wysocki" <rafael@xxxxxxxxxx> wrote: > > > On Sat, Sep 30, 2017 at 12:01 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> > > wrote: > > > intel idle driver does not DTRT when running within a VM: > > > when going into a deep power state, the right thing to > > > do is to exit to hypervisor rather than to keep polling > > > within guest using mwait. > > > > > > Currently the solution is just to exit to hypervisor each time we go > > > idle - this is why kvm does not expose the mwait leaf to guests even > > > when it allows guests to do mwait. > > > > > > But that's not ideal - it seems better to use the idle driver to > > > guess when will the next interrupt arrive. > > > > The idle driver alone is not sufficient for that, though. > > > I second that. Why try to solve this problem at vendor specific driver > level? Well we still want to e.g. mwait if possible - saves power. > perhaps just a pv idle driver that decide whether to vmexit > based on something like local per vCPU timer expiration? I guess we > can't predict other wake events such as interrupts. > e.g. > if (get_next_timer_interrupt() > kvm_halt_target_residency) > vmexit > else > poll > > Jacob It's not always a poll, on x86 putting the CPU in a low power state is possible within a VM. Does not seem possible on other CPUs that's why it's vendor specific. -- MST
