Vincent Guittot from Linaro Power Management Working Group discusses potential inputs for the scheduler to improve power management. These include: accurate load tracking of tasks, sharing of CPU clock speeds, sharing of idle states, accounting for shared caches, thermal constraints on CPUs, and keeping the scheduler simple to avoid performance penalties. Guittot covers approaches for determining load, clock speed, idle states, and thermal information to provide the scheduler. He asks for any other potential inputs and questions from attendees.

1. Vincent Guittot
Linaro Power Management Working Group
Which inputs for the scheduler ?
Vincent Guittot <vincent.guittot@linaro.org>
Linaro Power Management Working Group

2. Vincent Guittot
Linaro Power Management Working Group
Which inputs for the scheduler ?

Accurate load tracking

Sharing clock

Sharing Idle state

Sharing cache

Thermal constraint

Keep it simple

Others

3. Vincent Guittot
Linaro Power Management Working Group
Accurate load

Per task load tracking patch-set
– From Paul Turner
– Differentiate short and long running tasks
– Improve the task load migration

tick_sched monitors idle/run time
– /proc/stat
– cpufreq load monitoring

Unify load monitoring

4. Vincent Guittot
Linaro Power Management Working Group
CPU clock

Get the clock sharing topology
– Which CPUs share the same clock
– Helpful for power saving
– cpufreq has got such information
• cpus and cpus_related mask

Get current clock rate of a CPU
– Useful for more accurate load tracking

5. Vincent Guittot
Linaro Power Management Working Group
CPU idle

Get the idle state sharing topology
– Which CPUs shares their idle states level

Get the current idle state of a CPU
– Improve both performance and powersaving

How many level is needed ?
– Keep it as simple as a cpumask
●
Coupled cpuidle provide such information
– Make it more generic at cpuidle core level ?

6. Vincent Guittot
Linaro Power Management Working Group
Cache

Included in the share resources flag
– Currently the MC level
– Is it always true for ARM ?

7. Vincent Guittot
Linaro Power Management Working Group
Thermal

Thermal constraint on CPU
– Reduce Max freq → reduce cpu_power
– Depend of the time scale

8. Vincent Guittot
Linaro Power Management Working Group
Keep it simple

Scheduler performance is sensible
– Avoid large X*Y matrix computation
– Make it as simple a CPU mask manipulation

9. Vincent Guittot
Linaro Power Management Working Group
Other

Any other input ?

10. Vincent Guittot
Linaro Power Management Working Group
QUESTIONS ?

11. Vincent Guittot
Linaro Power Management Working Group
THANK YOU