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. 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. > +} > +
