On Tue, Oct 03, 2017 at 11:02:55PM +0200, Thomas Gleixner wrote: > On Mon, 2 Oct 2017, 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? 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) > > Bah. no. get_next_timer_interrupt() is not available for abuse in random > cpuidle driver code. It has state and its tied to the nohz code. > > There is the series from Audrey which makes use of the various idle > prediction mechanisms, scheduler, irq timings, idle governor to get an idea > about the estimated idle time. Exactly this information can be fed to the > kvmidle driver which can act accordingly. > > Hacking a random hardware specific idle driver is definitely the wrong > approach. It might be useful to chain the kvmidle driver and hardware > specific drivers at some point, i.e. if the kvmdriver decides not to exit > it delegates the mwait decision to the proper hardware driver in order not > to reimplement all the required logic again. By making changes to idle core to allow that chaining? Does this sound like something reasonable? > But that's a different story. > > See http://lkml.kernel.org/r/1506756034-6340-1-git-send-email-aubrey.li@xxxxxxxxx Will read that, thanks a lot. > Thanks, > > tglx > > >
