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SubjectRe: [RFC][PATCH 3/8] sched: update the cpu_power sum during load-balance
On Tue, Sep 01, 2009 at 10:34:34AM +0200, Peter Zijlstra wrote:
> In order to prepare for a more dynamic cpu_power, update the group sum
> while walking the sched domains during load-balance.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> kernel/sched.c | 33 +++++++++++++++++++++++++++++----
> 1 file changed, 29 insertions(+), 4 deletions(-)
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -3699,6 +3699,28 @@ static inline int check_power_save_busie
> }
> #endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
>
> +static void update_sched_power(struct sched_domain *sd)
> +{
> + struct sched_domain *child = sd->child;
> + struct sched_group *group, *sdg = sd->groups;
> + unsigned long power = sdg->__cpu_power;
> +
> + if (!child) {
> + /* compute cpu power for this cpu */
> + return;
> + }
> +
> + sdg->__cpu_power = 0;
> +
> + group = child->groups;
> + do {
> + sdg->__cpu_power += group->__cpu_power;
> + group = group->next;
> + } while (group != child->groups);
> +
> + if (power != sdg->__cpu_power)
> + sdg->reciprocal_cpu_power = reciprocal_value(sdg->__cpu_power);
> +}
>
> /**
> * update_sg_lb_stats - Update sched_group's statistics for load balancing.
> @@ -3712,7 +3734,8 @@ static inline int check_power_save_busie
> * @balance: Should we balance.
> * @sgs: variable to hold the statistics for this group.
> */
> -static inline void update_sg_lb_stats(struct sched_group *group, int this_cpu,
> +static inline void update_sg_lb_stats(struct sched_domain *sd,
> + struct sched_group *group, int this_cpu,
> enum cpu_idle_type idle, int load_idx, int *sd_idle,
> int local_group, const struct cpumask *cpus,
> int *balance, struct sg_lb_stats *sgs)
> @@ -3723,8 +3746,11 @@ static inline void update_sg_lb_stats(st
> unsigned long sum_avg_load_per_task;
> unsigned long avg_load_per_task;
>
> - if (local_group)
> + if (local_group) {
> balance_cpu = group_first_cpu(group);
> + if (balance_cpu == this_cpu)
> + update_sched_power(sd);
> + }

I guess the intention of this check is to ensure that the cpu_power for
the group of sd is updated only by a specific member of the group and
that would ideally be the first member of the group.

Thus, this check has more to do with this_cpu being the
group_first_cpu() than this_cpu being the balance_cpu. Correct ?

>
> /* Tally up the load of all CPUs in the group */
> sum_avg_load_per_task = avg_load_per_task = 0;
> @@ -3828,7 +3854,7 @@ static inline void update_sd_lb_stats(st
> local_group = cpumask_test_cpu(this_cpu,
> sched_group_cpus(group));
> memset(&sgs, 0, sizeof(sgs));
> - update_sg_lb_stats(group, this_cpu, idle, load_idx, sd_idle,
> + update_sg_lb_stats(sd, group, this_cpu, idle, load_idx, sd_idle,
> local_group, cpus, balance, &sgs);
>
> if (local_group && balance && !(*balance))
> @@ -3863,7 +3889,6 @@ static inline void update_sd_lb_stats(st
> update_sd_power_savings_stats(group, sds, local_group, &sgs);
> group = group->next;
> } while (group != sd->groups);
> -
> }
>
> /**
>
> --

--
Thanks and Regards
gautham


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