Messages in this thread | | | Date | Mon, 15 Dec 2008 12:31:39 +0530 | From | Balbir Singh <> | Subject | Re: [RFC PATCH v5 4/7] sched: bias task wakeups to preferred semi-idle packages |
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* Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> [2008-12-11 23:13:04]:
> Preferred wakeup cpu (from a semi idle package) has been > nominated in find_busiest_group() in the previous patch. Use > this information in sched_mc_preferred_wakeup_cpu in function > wake_idle() to bias task wakeups if the following conditions > are satisfied: > - The present cpu that is trying to wakeup the process is > idle and waking the target process on this cpu will > potentially wakeup a completely idle package > - The previous cpu on which the target process ran is > also idle and hence selecting the previous cpu may > wakeup a semi idle cpu package > - The task being woken up is allowed to run in the > nominated cpu (cpu affinity and restrictions) > > Basically if both the current cpu and the previous cpu on > which the task ran is idle, select the nominated cpu from semi > idle cpu package for running the new task that is waking up. > > Cache hotness is considered since the actual biasing happens > in wake_idle() only if the application is cache cold. > > This technique will effectively move short running bursty jobs in > a mostly idle system. > > Wakeup biasing for power savings gets automatically disabled if > system utilisation increases due to the fact that the probability > of finding both this_cpu and prev_cpu idle decreases. > > Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> > --- > > kernel/sched_fair.c | 17 +++++++++++++++++ > 1 files changed, 17 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > index 98345e4..939f2a1 100644 > --- a/kernel/sched_fair.c > +++ b/kernel/sched_fair.c > @@ -1027,6 +1027,23 @@ static int wake_idle(int cpu, struct task_struct *p) > cpumask_t tmp; > struct sched_domain *sd; > int i; > + unsigned int chosen_wakeup_cpu; > + int this_cpu; > + > + /* > + * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu > + * are idle and this is not a kernel thread and this task's affinity > + * allows it to be moved to preferred cpu, then just move! > + */ > + > + this_cpu = smp_processor_id(); > + chosen_wakeup_cpu = > + cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu; > + > + if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP && > + idle_cpu(cpu) && idle_cpu(this_cpu) && p->mm &&
The p->mm check is racy, it needs to be done under task_lock(). The best way to check for a kernel thread is get_task_mm(), followed by put_task_mm() is the mm is not NULL. We also need to check to see if the task is _hot_ on cpu. We should negate this optimization in case chosen_wakeup_cpu is idle, so check for that as well.
> + cpu_isset(chosen_wakeup_cpu, p->cpus_allowed)) > + return chosen_wakeup_cpu; > > /* > * If it is idle, then it is the best cpu to run this task. > >
-- Balbir
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