Messages in this thread Patch in this message |  | | | From | Vaidyanathan Srinivasan <> | | Subject | [RFC PATCH v3 3/5] sched: nominate preferred wakeup cpu | | Date | Tue, 11 Nov 2008 00:03:26 +0530 |
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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. For now lets try with a per-cpu variable pointing to a common storage in partition sched domain attribute. Global variable may not work in partitioned sched domain case.
Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> --- include/linux/sched.h | 1 + kernel/sched.c | 34 +++++++++++++++++++++++++++++++++- 2 files changed, 34 insertions(+), 1 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 715028a..8363d02 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -810,6 +810,7 @@ enum sched_domain_level { struct sched_domain_attr { int relax_domain_level; + unsigned int preferred_wakeup_cpu; }; #define SD_ATTR_INIT (struct sched_domain_attr) { \ diff --git a/kernel/sched.c b/kernel/sched.c index d910496..16c5e1f 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1612,6 +1612,21 @@ static void cfs_rq_set_shares(struct cfs_rq *cfs_rq, unsigned long shares) } #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). + */ + +DEFINE_PER_CPU(unsigned int *, sched_mc_preferred_wakeup_cpu); + +/* Default storage allocation for non-partitioned sched domains */ +unsigned int fallback_preferred_wakeup_cpu; + +#endif + #include "sched_stats.h" #include "sched_idletask.c" #include "sched_fair.c" @@ -3078,6 +3093,7 @@ 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 @@ -3394,6 +3410,10 @@ out_balanced: if (this == group_leader && group_leader != group_min) { *imbalance = min_load_per_task; + if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) + *per_cpu(sched_mc_preferred_wakeup_cpu, + smp_processor_id()) = + first_cpu(group_leader->cpumask); return group_min; } #endif @@ -7372,7 +7392,7 @@ static void set_domain_attribute(struct sched_domain *sd, static int __build_sched_domains(const cpumask_t *cpu_map, struct sched_domain_attr *attr) { - int i; + int i, cpu; struct root_domain *rd; SCHED_CPUMASK_DECLARE(allmasks); cpumask_t *tmpmask; @@ -7472,6 +7492,18 @@ static int __build_sched_domains(const cpumask_t *cpu_map, sd->parent = p; p->child = sd; cpu_to_core_group(i, cpu_map, &sd->groups, tmpmask); + /* Set the preferred wake up CPU */ + if (attr) { + for_each_cpu_mask_nr(cpu, sd->span) { + per_cpu(sched_mc_preferred_wakeup_cpu, cpu) = + &attr->preferred_wakeup_cpu; + } + } else { + for_each_cpu_mask_nr(cpu, sd->span) { + per_cpu(sched_mc_preferred_wakeup_cpu, cpu) = + &fallback_preferred_wakeup_cpu; + } + } #endif #ifdef CONFIG_SCHED_SMT
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