Re: [RFC][PATCH 15/16] sched: Trivial forced-newidle balancer

[Aubrey Li]

On Fri, Feb 22, 2019 at 12:42 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Thu, Feb 21, 2019 at 04:19:46PM +0000, Valentin Schneider wrote:
> > Hi,
> >
> > On 18/02/2019 16:56, Peter Zijlstra wrote:
> > [...]
> > > +static bool try_steal_cookie(int this, int that)
> > > +{
> > > +   struct rq *dst = cpu_rq(this), *src = cpu_rq(that);
> > > +   struct task_struct *p;
> > > +   unsigned long cookie;
> > > +   bool success = false;
> > > +
> > > +   local_irq_disable();
> > > +   double_rq_lock(dst, src);

Here, should we check dst and src's rq status before lock their rq?
if src is idle, it could be in the progress of load balance already?

Thanks,
-Aubrey

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3e3162f..a1e0a6f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3861,6 +3861,13 @@ static bool try_steal_cookie(int this, int that)
        unsigned long cookie;
        bool success = false;

+       /*
+        * Don't steal if src is idle or has only one runnable task,
+        * or dst has more than one runnable task
+        */
+       if (src->nr_running <= 1 || unlikely(dst->nr_running >= 1))
+               return false;
+
        local_irq_disable();
        double_rq_lock(dst, src);