On Mon, 5 Mar 2018 10:01:01 +1100
Paul Mackerras <pau...@ozlabs.org> wrote:
> On Thu, Mar 01, 2018 at 09:57:34PM +1000, Nicholas Piggin wrote:
> > On Thu, 1 Mar 2018 00:04:39 +0530
> > Vaidyanathan Srinivasan <sva...@linux.vnet.ibm.com> wrote:
> >
> > > * Nicholas Piggin <npig...@gmail.com> [2017-11-18 00:08:07]:
> [snip]
> > > > diff --git a/arch/powerpc/platforms/powernv/idle.c
> > > > b/arch/powerpc/platforms/powernv/idle.c
> > > > index a921d5428d76..610b1637c16f 100644
> > > > --- a/arch/powerpc/platforms/powernv/idle.c
> > > > +++ b/arch/powerpc/platforms/powernv/idle.c
> > > > @@ -621,7 +621,12 @@ static int __init pnv_power9_idle_init(struct
> > > > device_node *np, u32 *flags,
> > > > continue;
> > > > }
> > > >
> > > > - if (max_residency_ns < residency_ns[i]) {
> > > > + /*
> > > > + * Deepest stop for unplug must be PSSCR[EC]=1 (wakeup
> > > > at
> > > > + * 0x100.
> > > > + */
> > > > + if ((max_residency_ns < residency_ns[i])&&
> > > > + (psscr_val[i] & PSSCR_EC)) {
> > > > max_residency_ns = residency_ns[i];
> > > > pnv_deepest_stop_psscr_val = psscr_val[i];
> > > > pnv_deepest_stop_psscr_mask = psscr_mask[i];
> > >
> > > If firmware did not provide any ESL=EC=1 state, we can still leave
> > > threads in stop ESL=0 state. This is just a corner case or random
> > > test scenario. Why do we want to enforce that offline cpus really use
> > > a ESL=0 state or just spin?
> >
> > It's because power9_offline_stop only has cases for EC=ESL=1
> > states now.
> >
> > It actually looks like EC=ESL=0 unplug today is broken KVM, because
> > the wakeup side does not check HWTHREAD_REQ, and yet they do set
> > HWTHREAD_IN_IDLE. That would probably hang in KVM if we run with
> > dependent threads, wouldn't it?
>
> Right. KVM with indep_threads_mode=N is broken at the moment if you
> run with powersave=off or if firmware provides no stop states with
> EC=ESL=1. I'm not sure what's the best way to fix that.
For EC=ESL=1, would it be enough to do a test and branch right
after the stop instruction?
> > I think banning it for now should be okay.
>
> Banning what exactly?
power9 CPU unplug using a EC=ESL=0 stop state.
Thanks,
Nick
