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SubjectRe: [RFC PATCH v4 3/7] sched: nominate preferred wakeup cpu
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On Fri, 2008-11-21 at 14:01 +0530, Vaidyanathan Srinivasan wrote:
> When the system utilisation is low and more cpus are idle,
> then the process waking up from sleep should prefer to
> wakeup an idle cpu from semi-idle cpu package (multi core
> package) rather than a completely idle cpu package which
> would waste power.
>
> Use the sched_mc balance logic in find_busiest_group() to
> nominate a preferred wakeup cpu.
>
> This info can be sored in appropriate sched_domain, but
> updating this info in all copies of sched_domain is not
> practical. Hence this information is stored in root_domain
> struct which is one copy per partitioned sched domain.
> The root_domain can be accessed from each cpu's runqueue
> and there is one copy per partitioned sched domain.
>
> Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
> ---
>
> kernel/sched.c | 15 +++++++++++++++
> 1 files changed, 15 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 79b71f3..d28cd98 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -493,6 +493,17 @@ struct root_domain {
> #ifdef CONFIG_SMP
> struct cpupri cpupri;
> #endif
> +#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
> +
> + /*
> + * Preferred wake up cpu nominated by sched_mc balance that will be
> + * used when most cpus are idle in the system indicating overall very
> + * low system utilisation. Triggered at POWERSAVINGS_BALANCE_WAKEUP(2)
> + */
> + unsigned int sched_mc_preferred_wakeup_cpu;
> +
> +#endif
> +
> };
>
> /*

Do we really need that extra whitespace?

> @@ -3090,6 +3101,7 @@ static int move_one_task(struct rq *this_rq, int this_cpu, struct rq *busiest,
> return 0;
> }
>
> +
> /*
> * find_busiest_group finds and returns the busiest CPU group within the
> * domain. It calculates and returns the amount of weighted load which

Ditto?

> @@ -3406,6 +3418,9 @@ out_balanced:
>
> if (this == group_leader && group_leader != group_min) {
> *imbalance = min_load_per_task;
> + if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP)
> + cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
> + first_cpu(group_leader->cpumask);

While not strictly needed, I prefer braces around multi-line statments.
It's easier on the eyes.

> return group_min;
> }
> #endif
>



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