Re: [Patch v9 3/8] arm,arm64,drivers:Add infrastructure to store and update instantaneous thermal pressure

[Amit Kucheria]

On Thu, Feb 13, 2020 at 7:35 PM Thara Gopinath
<thara.gopinath@xxxxxxxxxx> wrote:
>
> On 02/13/2020 07:25 AM, Amit Kucheria wrote:
> > On Wed, Jan 29, 2020 at 4:06 AM Thara Gopinath
> > <thara.gopinath@xxxxxxxxxx> wrote:
> >>
> >> Add architecture specific APIs to update and track thermal pressure on a
> >> per cpu basis. A per cpu variable thermal_pressure is introduced to keep
> >> track of instantaneous per cpu thermal pressure. Thermal pressure is the
> >> delta between maximum capacity and capped capacity due to a thermal event.
> >
> > s/capped/decreased to have consistent use throughout the series e.g. in patch 1.
> >
> > Though personally, I like "capped capacity"  in which case
> > s/decreased/capped in patch 1 and elsewhere.
>
> I will fix this
> >
> >>
> >> topology_get_thermal_pressure can be hooked into the scheduler specified
> >> arch_cpu_thermal_capacity to retrieve instantaneous thermal pressure of a
> >> cpu.
> >>
> >> arch_set_thermal_pressure can be used to update the thermal pressure.
> >>
> >> Considering topology_get_thermal_pressure reads thermal_pressure and
> >> arch_set_thermal_pressure writes into thermal_pressure, one can argue for
> >> some sort of locking mechanism to avoid a stale value.  But considering
> >> topology_get_thermal_pressure can be called from a system critical path
> >> like scheduler tick function, a locking mechanism is not ideal. This means
> >> that it is possible the thermal_pressure value used to calculate average
> >> thermal pressure for a cpu can be stale for upto 1 tick period.
> >>
> >> Signed-off-by: Thara Gopinath <thara.gopinath@xxxxxxxxxx>
> >> ---
> >>
> >> v6->v7:
> >>         - Changed the input argument in arch_set_thermal_pressure from
> >>           capped capacity to delta capacity(thermal pressure) as per
> >>           Ionela's review comments.
> >>
> >>  arch/arm/include/asm/topology.h   |  3 +++
> >>  arch/arm64/include/asm/topology.h |  3 +++
> >
> > Any particular reason to enable this for arm/arm64 in this patch
> > itself? I'd have enabled them in two separate patches after this one.
>
> No reason. No reason not to as well as arch_topology is "Arm specific
> cpu topology file" and changes are one-liners.

One reason to do this, IMHO, is to keep platform conversions separate
from the core infrastructure in a series, so the core can get merged
while platform maintainers can take their time to decide if, when, how
to merge this.