Re: sched: Improve load balancing in the presence of idle CPUs

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

> > >
> > >  #ifdef CONFIG_NO_HZ_COMMON
> > > +static inline bool nohz_kick_needed(struct rq *rq);
> > > +
> > > +static inline void pass_nohz_balance(struct rq *this_rq, int this_cpu)
> > > +{
> > > +	clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
> > > +	nohz.next_balance = jiffies;
> >
> > Why are we updating nohz.next_balance here?
>
> This was just to make sure that since we're continuing the balancing on
> another CPU that the nohz next_balance is guaranteed to be "now".
>

Since we are in nohz_idle_balance(), nohz.next_balance is guaranteed be
less than now. We do check for time_before(now, nohz.next_balance) in
nohz_kick_needed(). So in effect we are incrementing the nohz.next_balance.

While updating nohz.next_balance may not cause any issues, it atleast
look redundant to me.

At this point, I also wanted to understand why we do
"nohz.next_balance++" nohz_balancer_kick()?


> > > +	if (nohz_kick_needed(this_rq))
> > > +		nohz_balancer_kick();
> > > +}
> > > +
> > >  /*

--
Thanks and Regards
Srikar Dronamraju