[PATCH 2/3] perf: add OMAP support for the new power events

Thomas Renninger [off-list ref] writes:

On Wednesday 05 January 2011 12:05:18 Jean Pihet wrote:

quoted

Hi Paul,

On Tue, Jan 4, 2011 at 7:48 PM, Paul Walmsley [off-list ref] wrote:

quoted

Hello Jean,

On Tue, 4 Jan 2011, jean.pihet at newoldbits.com wrote:

quoted

From: Jean Pihet <redacted>

The patch adds the new power management trace points for
the OMAP architecture.

The trace points are for:
- default idle handler. Since the cpuidle framework is
  instrumented in the generic way there is no need to
  add trace points in the OMAP specific cpuidle handler;
- cpufreq (DVFS),
- clocks changes (enable, disable, set_rate),

A question about these.  Are these only meant to track calls to these
functions from outside the clock code?  Or meant to track actual hardware
clock changes?

The former: this is used to track the clock requests from outside the
clock framework.

quoted

If the latter, then it might make sense to put these
trace points into the functions that actually change the hardware
registers, e.g., omap2_dflt_clk_{enable,disable}(), etc., since a
clk_enable() on a leaf clock may result in many internal system clocks
being enabled up the clock tree.

I agree with you it is better to track the actual clock changes instead.
I propose to move the tracepoints to omap2_clk_{enable...} which
enables all the clocks irrespectively of the installed handler.
Note about the clock handlers: omap2_dflt_clk_enable happens to be the
handler for all controllable clocks but could that change in the
future?

Looks like there is cpuidle34xx using cpuidle framework on specific
boards only.  And pm34xx.c and others override pm_idle and use the
same low level functions to reduce power consumption as cpuidle34xx.
Ideally pm34xx.c (and others) would not override pm_idle, but register as
a cpuidle driver. Then the idle events would be tracked by the
cpuidle subsystem automatically (with my latest patches).
But this would be a more intrusive change (are there efforts to do that?).

Whenever CPUidle is enabled though, the cpuidle34xx code is used so the
pm_idle in pm34xx is not used. This allows us to have a way to do PM
with and without CPUidle, so without CPUidle, we can still get some
basic PM in idle.

Even if it should happen at some point, adding some additional events for
people to better debug/monitor the stuff now does not hurt.

I agree, as the two both very useful.

Tracking CPUidle transitions gives us some high-level information on PM
transitions, but what is most interesting for real PM analysis on OMAP
is exactly which powerdomains, clockdomains and clocks transitions (or
didn't transition) for a given state.

Kevin