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SubjectRe: [patch v7 05/21] sched: log the cpu utilization at rq
[Apologies if threading mangled, all headers written by hand]

On 04/04/2013 07:30 AM, Alex Shi wrote:
> The cpu's utilization is to measure how busy is the cpu.
> util = cpu_rq(cpu)->avg.runnable_avg_sum * SCHED_POEWR_SCALE
> / cpu_rq(cpu)->avg.runnable_avg_period;
>
> Since the util is no more than 1, we scale its value with 1024, same as
> SCHED_POWER_SCALE and set the FULL_UTIL as 1024.
>
> In later power aware scheduling, we are sensitive for how busy of the
> cpu. Since as to power consuming, it is tight related with cpu busy
> time.
>
> BTW, rq->util can be used for any purposes if needed, not only power
> scheduling.
>
> Signed-off-by: Alex Shi <alex.shi@intel.com>
> ---
> include/linux/sched.h | 2 +-
> kernel/sched/debug.c | 1 +
> kernel/sched/fair.c | 5 +++++
> kernel/sched/sched.h | 4 ++++
> 4 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 5a4cf37..226a515 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -793,7 +793,7 @@ enum cpu_idle_type {
> #define SCHED_LOAD_SCALE (1L << SCHED_LOAD_SHIFT)
>
> /*
> - * Increase resolution of cpu_power calculations
> + * Increase resolution of cpu_power and rq->util calculations
> */
> #define SCHED_POWER_SHIFT 10
> #define SCHED_POWER_SCALE (1L << SCHED_POWER_SHIFT)
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 75024a6..f5db759 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -311,6 +311,7 @@ do { \
>
> P(ttwu_count);
> P(ttwu_local);
> + P(util);
>
> #undef P
> #undef P64
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 2e49c3f..7124244 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1495,8 +1495,13 @@ static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq, int force_update)
>
> static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
> {
> + u32 period;
> __update_entity_runnable_avg(rq->clock_task, &rq->avg, runnable);
> __update_tg_runnable_avg(&rq->avg, &rq->cfs);
> +
> + period = rq->avg.runnable_avg_period ? rq->avg.runnable_avg_period : 1;
> + rq->util = (u64)(rq->avg.runnable_avg_sum << SCHED_POWER_SHIFT)
> + / period;

Greetings, Alex.

That cast achieves nothing where it is. If the shift has overflowed,
then you've already lost information; and if it can't overflow, then
it's not needed at all.

It's itsy-bitsy, but note that there exists a div_u64(u64 dividend,
u32 divisor) helper which may be implemented to be superior to just '/'.
(And also note that the assignment to ``period'' is a good candidate for
gcc's ``?:'' operator.)

If you pull the cast inside the brackets, then you may add my
Reviewed-by: Phil Carmody <pc+lkml@asdf.org>

Cheers,
Phil

> }
>
> /* Add the load generated by se into cfs_rq's child load-average */
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 804ee41..8682110 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -351,6 +351,9 @@ extern struct root_domain def_root_domain;
>
> #endif /* CONFIG_SMP */
>
> +/* full cpu utilization */
> +#define FULL_UTIL SCHED_POWER_SCALE
> +
> /*
> * This is the main, per-CPU runqueue data structure.
> *
> @@ -482,6 +485,7 @@ struct rq {
> #endif
>
> struct sched_avg avg;
> + unsigned int util;
> };
>
> static inline int cpu_of(struct rq *rq)
>
--
"In a world of magnets and miracles"
-- Insane Clown Posse, Miracles, 2009. Much derided.
"Magnets, how do they work"
-- Pink Floyd, High Hopes, 1994. Lauded as lyrical geniuses.


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