On Fri, 12 Feb 2021 at 20:19, Valentin Schneider <[email protected]> wrote: > > On 12/02/21 15:17, Vincent Guittot wrote: > > Instead of waking up a random and already idle CPU, we can take advantage > > of this_cpu being about to enter idle to run the ILB and update the > > blocked load. > > > > Signed-off-by: Vincent Guittot <[email protected]> > > --- > > kernel/sched/fair.c | 24 +++++++++++++++++++++--- > > kernel/sched/idle.c | 6 ++++++ > > kernel/sched/sched.h | 5 +++++ > > 3 files changed, 32 insertions(+), 3 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 5d285d93e433..cd0ea635225e 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -10453,6 +10453,24 @@ static bool nohz_idle_balance(struct rq *this_rq, > > enum cpu_idle_type idle) > > return true; > > } > > > > +/* > > + * Check if we need to run the ILB for updating blocked load before > > entering > > + * idle state. > > + */ > > +void nohz_run_idle_balance(int cpu) > > +{ > > + unsigned int flags; > > + > > + flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(cpu)); > > + > > + if (flags && !need_resched()) { > > + struct rq *rq = cpu_rq(cpu); > > + > > + rq->nohz_idle_balance = flags; > > + nohz_idle_balance(rq, CPU_IDLE); > > + } > > So this can now run a full fledged nohz_idle_balance() if NOHZ_BALANCE_MASK > is set.
Yes. > > I don't think there is anything inherently wrong with it - the > nohz_idle_balance() call resulting from the kick_ilb() IPI will just bail > out due to the flags being cleared here. This wasn't immediately clear to > me however. In fact, I forgot to replace the WARN_ON in nohz_csd_func() by a simple return as reported by kernel test robot / [email protected] > > > +} > > +
