Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Rate limit calls to update_blocked_averages() for NOHZ | From | Tim Chen <> | Date | Wed, 24 Mar 2021 09:05:45 -0700 |
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On 3/24/21 6:44 AM, Vincent Guittot wrote: > Hi Tim,
> > IIUC your problem, we call update_blocked_averages() but because of: > > if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost) { > update_next_balance(sd, &next_balance); > break; > } > > the for_each_domain loop stops even before running load_balance on the 1st > sched domain level which means that update_blocked_averages() was called > unnecessarily. >
That's right
> And this is even more true with a small sysctl_sched_migration_cost which allows newly > idle LB for very small this_rq->avg_idle. We could wonder why you set such a low value > for sysctl_sched_migration_cost which is lower than the max_newidle_lb_cost of the > smallest domain but that's probably because of task_hot(). > > if avg_idle is lower than the sd->max_newidle_lb_cost of the 1st sched_domain, we should > skip spin_unlock/lock and for_each_domain() loop entirely > > Maybe something like below: >
The patch makes sense. I'll ask our benchmark team to queue this patch for testing.
Tim
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