| Date | Wed, 24 Feb 2021 16:53:54 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 0/7 v4] move update blocked load outside newidle_balance |
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On Wed, Feb 24, 2021 at 02:30:00PM +0100, Vincent Guittot wrote: > Joel reported long preempt and irq off sequence in newidle_balance because > of a large number of CPU cgroups in use and having to be updated. This > patchset moves the update outside newidle_imblance. This enables to early > abort during the updates in case of pending irq as an example. > > Instead of kicking a normal ILB that will wakes up CPU which is already > idle, patch 6 triggers the update of statistics in the idle thread of > the CPU before selecting and entering an idle state.
I'm confused... update_blocked_averages(), which calls __update_blocked_fair(), which is the one doing the cgroup iteration thing, runs with rq->lock held, and thus will have IRQs disabled any which way around we turn this thing.
Or is the problem that we called nohz_idle_balance(), which does update_nohz_stats() -> update_blocked_averages() for evey NOHZ cpu from newidle balance, such that we get NR_NOHZ_CPUS * NR_CGROUPS IRQ latency? Which is now reduced to just NR_CGROUPS ?
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