On Fri, May 30, 2014 at 03:04:32PM +0100, Dietmar Eggemann wrote:
On 23/05/14 16:52, Vincent Guittot wrote:
power_orig is only changed for system with a SMT sched_domain level in order to reflect the lower capacity of CPUs. Heterogenous system also have to reflect an original capacity that is different from the default value.
Create a more generic function arch_scale_cpu_power that can be also used by non SMT platform to set power_orig.
The weak behavior of arch_scale_cpu_power is the previous SMT one in order to keep backward compatibility in the use of power_orig.
Signed-off-by: Vincent Guittot vincent.guittot@linaro.org
As you know, besides uarch scaled cpu power for HMP, freq scaled cpu power is important for energy-aware scheduling to achieve freq scale invariance for task load.
I know that your patch-set is not about introducing freq scaled cpu power, but we were discussing how this can be achieved w/ your patch-set in place, so maybe you can share your opinion regarding the easiest way to achieve freq scale invariance with us?
(1) We assume that the current way (update_cpu_power() calls arch_scale_freq_power() to get the avg power(freq) over the time period since the last call to arch_scale_freq_power()) is suitable for us. Do you have another opinion here?
(2) Is the current layout of update_cpu_power() adequate for this, where we scale power_orig related to freq and then related to rt/(irq):
power_orig = scale_cpu(SCHED_POWER_SCALE) power = scale_rt(scale_freq(power_orig))
or do we need an extra power_freq data member on the rq and do:
power_orig = scale_cpu(SCHED_POWER_SCALE) power_freq = scale_freq(power_orig)) power = scale_rt(power_orig))
In other words, do we consider rt/(irq) pressure when calculating freq scale invariant task load or not?
I don't think you should. The work done depends on the frequency, not on other tasks present on the cpu. The same is true for an over-utilized cpu, a task will run less than the desired amount of time, this is no different from a RT/irq preempting the task and taking its time.