Re: [CFS Bandwidth Control v4 1/7] sched: introduce primitives to account for CFS bandwidth tracking

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Wed, Feb 16, 2011 at 10:22:16PM +0530, Balbir Singh wrote:
> * Paul Turner <pjt@google.com> [2011-02-15 19:18:32]:
> 
> > In this patch we introduce the notion of CFS bandwidth, to account for the
> > realities of SMP this is partitioned into globally unassigned bandwidth, and
> > locally claimed bandwidth:
> > - The global bandwidth is per task_group, it represents a pool of unclaimed
> >   bandwidth that cfs_rq's can allocate from.  It uses the new cfs_bandwidth
> >   structure.
> > - The local bandwidth is tracked per-cfs_rq, this represents allotments from
> >   the global pool
> >   bandwidth assigned to a task_group, this is tracked using the
> >   new cfs_bandwidth structure.
> > 
> > Bandwidth is managed via cgroupfs via two new files in the cpu subsystem:
> > - cpu.cfs_period_us : the bandwidth period in usecs
> > - cpu.cfs_quota_us : the cpu bandwidth (in usecs) that this tg will be allowed
> >   to consume over period above.
> > 
> > A per-cfs_bandwidth timer is also introduced to handle future refresh at
> > period expiration.  There's some minor refactoring here so that
> > start_bandwidth_timer() functionality can be shared
> > 
> > Signed-off-by: Paul Turner <pjt@google.com>
> > Signed-off-by: Nikhil Rao <ncrao@google.com>
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > ---
> 
> Looks good, minor nits below
> 
> 
> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>

Thanks Balbir.

> > +
> > +static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
> > +{
> > +	struct cfs_bandwidth *cfs_b =
> > +		container_of(timer, struct cfs_bandwidth, period_timer);
> > +	ktime_t now;
> > +	int overrun;
> > +	int idle = 0;
> > +
> > +	for (;;) {
> > +		now = hrtimer_cb_get_time(timer);
> > +		overrun = hrtimer_forward(timer, now, cfs_b->period);
> > +
> > +		if (!overrun)
> > +			break;
> > +
> > +		idle = do_sched_cfs_period_timer(cfs_b, overrun);
> 
> This patch just sets up to return do_sched_cfs_period_timer to return
> 1. I am afraid I don't understand why this function is introduced
> here.

Answered this during last post: http://lkml.org/lkml/2010/10/14/31

> > +
> > +	mutex_lock(&mutex);
> > +	raw_spin_lock_irq(&tg->cfs_bandwidth.lock);
> > +	tg->cfs_bandwidth.period = ns_to_ktime(period);
> > +	tg->cfs_bandwidth.runtime = tg->cfs_bandwidth.quota = quota;
> > +	raw_spin_unlock_irq(&tg->cfs_bandwidth.lock);
> > +
> > +	for_each_possible_cpu(i) {
> 
> Why for each possible cpu - to avoid hotplug handling?

Touched upon this during last post: https://lkml.org/lkml/2010/12/6/49

Regards,
Bharata.