Messages in this thread | | | Date | Thu, 19 Mar 2009 22:53:52 +0530 | From | Vaidyanathan Srinivasan <> | Subject | Re: [PATCH 3 5/6] sched: Arbitrate the nomination of preferred_wakeup_cpu |
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* Gautham R Shenoy <ego@in.ibm.com> [2009-03-18 14:52:43]:
> Currently for sched_mc/smt_power_savings = 2, we consolidate tasks > by having a preferred_wakeup_cpu which will be used for all the > further wake ups. > > This preferred_wakeup_cpu is currently nominated by find_busiest_group() > while loadbalancing for sched_domains which has SD_POWERSAVINGS_BALANCE flag > set. > > However, on systems which are multi-threaded and multi-core, we can > have multiple sched_domains in the same hierarchy with > SD_POWERSAVINGS_BALANCE flag set. > > Currently we don't have any arbitration mechanism as to while load balancing > for which sched_domain in the hierarchy should find_busiest_group(sd) > nominate the preferred_wakeup_cpu. Hence can overwrite valid nominations > made previously thereby causing the preferred_wakup_cpu to ping-pong > thereby preventing us from effectively consolidating tasks. > > Fix this by means of an arbitration algorithm, where in we nominate the > preferred_wakeup_cpu sched_domain in find_busiest_group() for a particular > sched_domain if the sched_domain: > - is the topmost power aware sched_domain. > OR > - contains the previously nominated preferred wake up cpu in it's span. > > This will help to further fine tune the wake-up biasing logic by > identifying a partially busy core within a CPU package instead of > potentially waking up a completely idle core. > > Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> > --- > > kernel/sched.c | 45 +++++++++++++++++++++++++++++++++++++++++++-- > 1 files changed, 43 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched.c b/kernel/sched.c > index 16d7655..651550c 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -522,6 +522,14 @@ struct root_domain { > * This is triggered at POWERSAVINGS_BALANCE_WAKEUP(2). > */ > unsigned int preferred_wakeup_cpu; > + > + /* > + * top_powersavings_sd_lvl records the level of the highest > + * sched_domain that has the SD_POWERSAVINGS_BALANCE flag set. > + * > + * Used to arbitrate nomination of the preferred_wakeup_cpu. > + */ > + enum sched_domain_level top_powersavings_sd_lvl; > #endif > }; > > @@ -3416,9 +3424,27 @@ out_balanced: > goto ret; > > if (this == group_leader && group_leader != group_min) { > + struct root_domain *my_rd = cpu_rq(this_cpu)->rd; > *imbalance = min_load_per_task; > - if (active_power_savings_level >= POWERSAVINGS_BALANCE_WAKEUP) { > - cpu_rq(this_cpu)->rd->preferred_wakeup_cpu = > + /* > + * To avoid overwriting of preferred_wakeup_cpu nominations > + * while calling find_busiest_group() at various sched_domain > + * levels, we define an arbitration mechanism wherein > + * find_busiest_group() nominates a preferred_wakeup_cpu at > + * the sched_domain sd if: > + * > + * - sd is the highest sched_domain in the hierarchy having the > + * SD_POWERSAVINGS_BALANCE flag set. > + * > + * OR > + * > + * - sd contains the previously nominated preferred_wakeup_cpu > + * in it's span. > + */ > + if (sd->level == my_rd->top_powersavings_sd_lvl || > + cpu_isset(my_rd->preferred_wakeup_cpu, > + *sched_domain_span(sd))) { > + my_rd->preferred_wakeup_cpu = > cpumask_first(sched_group_cpus(group_leader)); > } > return group_min; > @@ -7541,6 +7567,8 @@ static int __build_sched_domains(const struct cpumask *cpu_map, > struct root_domain *rd; > cpumask_var_t nodemask, this_sibling_map, this_core_map, send_covered, > tmpmask; > + struct sched_domain *sd; > + > #ifdef CONFIG_NUMA > cpumask_var_t domainspan, covered, notcovered; > struct sched_group **sched_group_nodes = NULL; > @@ -7816,6 +7844,19 @@ static int __build_sched_domains(const struct cpumask *cpu_map, > > err = 0; > > + rd->preferred_wakeup_cpu = UINT_MAX; > + rd->top_powersavings_sd_lvl = SD_LV_NONE; > + > + if (active_power_savings_level < POWERSAVINGS_BALANCE_WAKEUP) > + goto free_tmpmask; > + > + /* Record the level of the highest power-aware sched_domain */ > + for_each_domain(first_cpu(*cpu_map), sd) { > + if (!(sd->flags & SD_POWERSAVINGS_BALANCE)) > + continue; > + rd->top_powersavings_sd_lvl = sd->level; > + } > + > free_tmpmask: > free_cpumask_var(tmpmask); > free_send_covered: >
Acked-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
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