Peter Zijlstra's on April 11, 2019 8:53 pm: > Was this supposed to be patch 6/5 of your previous series?
Dang, I screwed up the headers? Thanks for the ping, I will resend. It is standalone. It seems more suited to the scheduler tree than the timers one, but your call. It is generally of more use when CPU0 is _not_ a housekeeping one, and that's where I've done most testing, but I don't see any hard dependency. Thanks, Nick > > On Thu, Apr 11, 2019 at 04:05:36PM +1000, Nicholas Piggin wrote: >> Date: Tue, 9 Apr 2019 20:23:16 +1000 >> Subject: [PATCH] kernel/sched: run nohz idle load balancer on HK_FLAG_MISC >> CPUs >> >> The nohz idle balancer runs on the lowest idle CPU. This can >> interfere with isolated CPUs, so confine it to HK_FLAG_MISC >> housekeeping CPUs. >> >> HK_FLAG_SCHED is not used for this because it is not set anywhere >> at the moment. This could be folded into HK_FLAG_SCHED once that >> option is fixed. >> >> The problem was observed with increased jitter on an application >> running on CPU0, caused by nohz idle load balancing being run on >> CPU1 (an SMT sibling). >> >> Signed-off-by: Nicholas Piggin <npig...@gmail.com> >> --- >> kernel/sched/fair.c | 16 ++++++++++------ >> 1 file changed, 10 insertions(+), 6 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index fdab7eb6f351..d29ca323214d 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -9522,22 +9522,26 @@ static inline int on_null_domain(struct rq *rq) >> * - When one of the busy CPUs notice that there may be an idle rebalancing >> * needed, they will kick the idle load balancer, which then does idle >> * load balancing for all the idle CPUs. >> + * - HK_FLAG_MISC CPUs are used for this task, because HK_FLAG_SCHED not set >> + * anywhere yet. >> */ >> >> static inline int find_new_ilb(void) >> { >> - int ilb = cpumask_first(nohz.idle_cpus_mask); >> + int ilb; >> >> - if (ilb < nr_cpu_ids && idle_cpu(ilb)) >> - return ilb; >> + for_each_cpu_and(ilb, nohz.idle_cpus_mask, >> + housekeeping_cpumask(HK_FLAG_MISC)) { >> + if (idle_cpu(ilb)) >> + return ilb; >> + } >> >> return nr_cpu_ids; >> } >> >> /* >> - * Kick a CPU to do the nohz balancing, if it is time for it. We pick the >> - * nohz_load_balancer CPU (if there is one) otherwise fallback to any idle >> - * CPU (if there is one). >> + * Kick a CPU to do the nohz balancing, if it is time for it. We pick any >> + * idle CPU in the HK_FLAG_MISC housekeeping set (if there is one). >> */ >> static void kick_ilb(unsigned int flags) >> { >> -- >> 2.20.1 >> >