Re: [PATCH V2 3/3] sched: Move idle_stamp up to the core

[Daniel Lezcano]

On 02/10/2014 11:04 AM, Preeti Murthy wrote:
> Hi Daniel,
>
> On Fri, Feb 7, 2014 at 4:40 AM, Daniel Lezcano
> <daniel.lezcano@xxxxxxxxxx> wrote:
> > The idle_balance modifies the idle_stamp field of the rq, making this
> > information to be shared across core.c and fair.c. As we can know if the
> > cpu is going to idle or not with the previous patch, let's encapsulate the
> > idle_stamp information in core.c by moving it up to the caller. The
> > idle_balance function returns true in case a balancing occured and the cpu
> > won't be idle, false if no balance happened and the cpu is going idle.
> >
> > Cc: mingo@xxxxxxxxxx
> > Cc: alex.shi@xxxxxxxxxx
> > Cc: peterz@xxxxxxxxxxxxx
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> > Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > ---
> >   kernel/sched/core.c  |   13 +++++++++++--
> >   kernel/sched/fair.c  |   14 ++++++--------
> >   kernel/sched/sched.h |    8 +-------
> >   3 files changed, 18 insertions(+), 17 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 16b97dd..428ee4c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -2704,8 +2704,17 @@ need_resched:
> >
> >          pre_schedule(rq, prev);
> >
> > -       if (unlikely(!rq->nr_running))
> > -               idle_balance(rq);
> > +#ifdef CONFIG_SMP
> > +       if (unlikely(!rq->nr_running)) {
> > +               /*
> > +                * We must set idle_stamp _before_ calling idle_balance(), such
> > +                * that we measure the duration of idle_balance() as idle time.
>
> Should not this be "such that we *do not* measure the duration of idle_balance()
> as idle time?"

Actually, the initial code was including the idle balance time 
processing in the idle stamp. When I moved the idle stamp in core.c, 
idle balance was no longer measured (an unwanted change). That has been 
fixed and to prevent that to occur again, we added a comment.

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