Messages in this thread | | | Date | Tue, 5 Oct 2021 22:49:27 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] sched/fair: Skip update_blocked_averages if we are defering load balance |
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On Mon, Oct 04, 2021 at 07:14:51PM +0200, Vincent Guittot wrote: > In newidle_balance(), the scheduler skips load balance to the new idle cpu > when the 1st sd of this_rq is: > > this_rq->avg_idle < sd->max_newidle_lb_cost > > Doing a costly call to update_blocked_averages() will not be useful and > simply adds overhead when this condition is true. > > Check the condition early in newidle_balance() to skip > update_blocked_averages() when possible. > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> > --- > kernel/sched/fair.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 1f78b2e3b71c..1294b78503d9 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -10841,17 +10841,20 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) > */ > rq_unpin_lock(this_rq, rf); > > + rcu_read_lock(); > + sd = rcu_dereference_check_sched_domain(this_rq->sd); > + > if (this_rq->avg_idle < sysctl_sched_migration_cost || > - !READ_ONCE(this_rq->rd->overload)) { > + !READ_ONCE(this_rq->rd->overload) || > + (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
set cino=(0:0, please.
Also, people have, in the past, tried to get rid of the first clause here, perhaps this can replace it instead of augment it?
> > - rcu_read_lock(); > - sd = rcu_dereference_check_sched_domain(this_rq->sd); > if (sd) > update_next_balance(sd, &next_balance); > rcu_read_unlock(); > > goto out; > } > + rcu_read_unlock();
There's another rcu_read_lock section right below this, at the very least we can merge them.
Also, IIRC we're running all this with premption disabled, and since rcu-sched got folded into rcu, all that rcu_read_*lock() stuff isn't strictly required anymore.
(we're full circle there, back in the day RCU implied RCU-sched and the scheduler relied on preempt-disable for lots of this stuff, then Paul split them, and I spend a fair amount of time adding all this rcu_read_*lock() crud, and now he's merge them again, and it can go again).
Except of course, I think we need to make rcu_dereference_check happy first :/
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