Messages in this thread | | | Date | Mon, 15 Dec 2008 14:13:52 +0530 | From | Balbir Singh <> | Subject | Re: [RFC PATCH v5 4/7] sched: bias task wakeups to preferred semi-idle packages |
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* Peter Zijlstra <a.p.zijlstra@chello.nl> [2008-12-15 09:25:21]:
> On Mon, 2008-12-15 at 12:31 +0530, Balbir Singh wrote: > > > > 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. > > Sure its racy, but so what? > > The worst I can see it that we exclude a dying task from this logic, > which isn't a problem at all, since its dying anyway.
Fair enough... except that they dying task will wake up a potentially idle CPU and die.
> > Also, I don't think you can grab task_lock() from under rq->lock...
I've not looked at how task_lock() nests under rq->lock. I'll look
> > > > + 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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