[PATCH] arm64: dts: Add idle-states for Juno

[Catalin Marinas]

On Fri, May 01, 2015 at 11:12:11AM +0100, Lorenzo Pieralisi wrote:
> On Fri, May 01, 2015 at 10:02:02AM +0100, Catalin Marinas wrote:
> > On Thu, Apr 30, 2015 at 06:17:01PM +0100, Lorenzo Pieralisi wrote:
> > > On Thu, Apr 30, 2015 at 05:40:35PM +0100, Jon Medhurst (Tixy) wrote:
> > > > On Thu, 2015-04-30 at 17:00 +0100, Sudeep Holla wrote:
> > > > > On 30/04/15 14:57, Jon Medhurst (Tixy) wrote:
> > > > > > From: Jon Medhurst <tixy at linaro.org>
> > > > > >
> > > > > > Signed-off-by: Jon Medhurst <tixy at linaro.org>
> > > > > > ---
> > > > > >
> > > > > > These have been kicking around out of tree for ages, any reason they
> > > > > > shouldn't be in mainline?
> > > > > 
> > > > > One possible reason could be that these values are not tuned(e.g.
> > > > > latency values, can they be same for both clusters ?)
> > > > 
> > > > I thought that both clusters being the same was questionable.
> > > > 
> > > > >  Though these
> > > > > reasons are not blocking and this patch will not cause any
> > > > > functionality break even if is merged as is.
> > > > 
> > > > My main purpose with trying to get this merged is so that people using
> > > > Juno for general testing and validation will actually have cpuidle
> > > > running and so potentially find more bugs.
> > > 
> > > I am reluctant to enable idle states in the default Juno dts, they
> > > will affect latencies and performance tests significantly.
> > 
> > OTOH, I guess they will improve the power benchmarks. IMO, we should
> > place in the DT whatever the hardware and firmware supports. It's up to
> > those doing benchmarks to disable CPU suspend.
> 
> I am ok with DT defining whatever HW and FW support, the question is
> whether we want CPUidle (and CPUfreq) enabled by default in the
> defconfig then.

It's functionality we support, so I think it should be enabled in
defconfig. This config is meant as a point of reference for what's
supported by the arm64 kernel and not tuned for some specific
benchmarks.

> This will certainly trigger mainline regressions from a latency/performance
> standpoint (true, some tests disable idle states by default ie cyclic
> test), unless we disable CPUidle via command line parameter or we
> force people carrying out tests to disable idle states through sysfs knobs.

It may affect performance for specific benchmarks but what if others
test the power consumption?

BTW, cannot the cpuidle governor be made smart enough (unless it is
already) to figure out when the next timer is going to happen so that
the CPU doesn't go in a deep sleep state with a high latency?

-- 
Catalin