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    SubjectRe: [PATCH 0/7 v4] move update blocked load outside newidle_balance
    On Wed, 24 Feb 2021 at 16:54, Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > 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 ?

    Yes we can now abort between each cpu update

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