Re: [PATCH] powerpc/powernv/idle: Round up latency and residency values

[Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>]

* Michael Ellerman <mpe@ellerman.id.au> [2017-08-24 20:28:19]:

> Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> writes:
> 
> > On PowerNV platforms, firmware provides exit latency and
> > target residency for each of the idle states in nano
> > seconds.  Cpuidle framework expects the values in micro
> > seconds.  Round up to nearest micro seconds to avoid errors
> > in cases where the values are defined as fractional micro
> > seconds.
> >
> > Default idle state of 'snooze' has exit latency of zero.  If
> > other states have fractional micro second exit latency, they
> > would get rounded down to zero micro second and make cpuidle
> > framework choose deeper idle state when snooze loop is the
> > right choice.
> >
> > Reported-by: Anton Blanchard <anton@samba.org>
> > Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
> 
> This sounds like a fairly bad bug, does it need a Fixes / Cc stable tag?

Yes, we will need this on stable kernel that runs on POWER9.  On older
platforms the latencies are larger and hence no impact :)

I will post to stable after this fix hits your -next tree.

--Vaidy