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.
> I think banning it for now should be okay.
Banning what exactly?
Paul.
