Hi Jason, On 1 August 2015 at 00:12, Jason Low <[email protected]> wrote: > Hi Vincent, > > On Fri, 2015-07-31 at 11:49 +0200, Vincent Guittot wrote: >> Since commit d4573c3e1c99 ("sched: Improve load balancing in the presence >> of idle CPUs"), the ILB CPU starts with the idle load balancing of other >> idle CPUs and finishes with itself in order to speed up the spread of tasks >> in all idle CPUs. >> >> The this_rq->next_balance is still used in nohz_idle_balance as an >> intermediate step to gather the shortest next balance before updating >> nohz.next_balance. But the former has not been updated yet and is likely to >> be set with the current jiffies. As a result, the nohz.next_balance will be >> set with current jiffies instead of the real next balance date. This >> generates spurious kicks of nohz ilde balance. >> >> nohz_idle_balance must set the nohz.next_balance without taking into >> account this_rq->next_balance which is not updated yet. Then, this_rq will >> update nohz.next_update with its next_balance once updated and if necessary. >> >> Signed-off-by: Vincent Guittot <[email protected]> >> --- >> kernel/sched/fair.c | 33 +++++++++++++++++++++++++++++---- >> 1 file changed, 29 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 587a2f6..2b02089 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -7779,8 +7779,21 @@ static void rebalance_domains(struct rq *rq, enum >> cpu_idle_type idle) >> * When the cpu is attached to null domain for ex, it will not be >> * updated. >> */ >> - if (likely(update_next_balance)) >> + if (likely(update_next_balance)) { >> rq->next_balance = next_balance; >> + >> + /* >> + * If this cpu has been elected to perform the nohz idle >> + * balance. Other idle cpus have already rebalance with >> + * nohz_idle_balance and the nohz.next_balaance has been >> + * updated accordingly. This cpu has now run the idle load >> + * balance for itself and we need to update the >> + * nohz.next_balance accordingly. >> + */ >> + if ((idle == CPU_IDLE) && >> + time_after(nohz.next_balance, rq->next_balance)) >> + nohz.next_balance = rq->next_balance; > > The code accessing the "nohz" structure may also need to be put in an: > > #ifdef CONFIG_NO_HZ_COMMON > > in order for it to compile when !CONFIG_NO_HZ_COMMON.
You're right. I'm going to fix that right now Vincent > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
