Re: [PATCH 3 3/6] sched: Add Comments at the beginning of find_busiest_group.

[Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>]

* Gautham R Shenoy <ego@in.ibm.com> [2009-03-18 14:52:33]:

> Currently there are no comments pertaining to power-savings balance in
> the function find_busiest_group. Add appropriate comments.
> 
> Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---
> 
>  kernel/sched.c |   17 +++++++++++++++++
>  1 files changed, 17 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 407ee03..864c6ca 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -3090,6 +3090,23 @@ static int move_one_task(struct rq *this_rq, int this_cpu, struct rq *busiest,
>   * find_busiest_group finds and returns the busiest CPU group within the
>   * domain. It calculates and returns the amount of weighted load which
>   * should be moved to restore balance via the imbalance parameter.
> + *
> + * Power-savings-balance: Through the sysfs tunables sched_mc/smt_power_savings
> + * he user can opt for aggressive task consolidation as a means to save power.
      ^ the  
> + * When this is activated, we would have the SD_POWERSAVINGS_BALANCE flag
           ^^^^ When sched_{mc,smt}_powersavings is activated, then
           SD_POWERSAVINGS_BALANCE...
> + * set for appropriate sched_domains,
> + *
> + * Within such sched_domains, find_busiest_group would try to identify
> + * a sched_group which can be freed-up and whose tasks can be migrated to
> + * a sibling group which has the capacity to accomodate the former's tasks.
                                        ^^^ remaining capacity
> + * If such a "can-go-idle" sched_group does exist, then the sibling group
                                                                ^^^^^^^^
                                                this group is returned
                                                as busiest_group                                                                        
> + * which can accomodate it's tasks is returned as the busiest group.
                                ^^^^^^^^^^^^^^^^ This is the
                                group_leader and busiest_group is
                                returned if the current cpu is
                                a member of group leader.
> + *
> + * Furthermore, if the user opts for more aggressive power-aware load
> + * balancing through sched_smt/mc_power_savings = 2, i.e when the
> + * active_power_savings_level greater or equal to POWERSAVINGS_BALANCE_WAKEUP,
> + * find_busiest_group will also nominate the preferred CPU, on which the tasks
> + * should hence forth be woken up on, instead of bothering an idle-cpu.
>   */
>  static struct sched_group *
>  find_busiest_group(struct sched_domain *sd, int this_cpu,


Acked-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>