Messages in this thread | | | Date | Mon, 15 Dec 2008 12:10:56 +0530 | From | Balbir Singh <> | Subject | Re: [RFC PATCH v5 3/7] sched: nominate preferred wakeup cpu |
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* Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> [2008-12-11 23:12:57]:
> 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 | 12 ++++++++++++ > 1 files changed, 12 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched.c b/kernel/sched.c > index 6bea99b..0918677 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -493,6 +493,14 @@ 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)
Is the root domain good enough?
What is POWERSAVINGS_BALANCE_WAKEUP(2), is it sched_mc == 2?
> + */ > + unsigned int sched_mc_preferred_wakeup_cpu; > +#endif > }; > > /* > @@ -3407,6 +3415,10 @@ out_balanced: > > if (this == group_leader && group_leader != group_min) { > *imbalance = min_load_per_task; > + if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
OK, it is :) (for the question above). Where do we utilize the set sched_mc_preferred_wakeup_cpu?
> + cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu = > + first_cpu(group_leader->cpumask);
Everytime we balance, we keep replacing rd->sched_mc_preferred_wake_up with group_lead->cpumask? My big concern is that we do this without checking if the group_leader has sufficient capacity (after it will pull in tasks since we made the checks for nr_running and capacity).
> + } > return group_min; > } > #endif > >
-- Balbir
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