Messages in this thread | | | Date | Wed, 24 Feb 2021 18:41:09 +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 04:57:15PM +0100, Vincent Guittot wrote: > 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
OK, shall I add something like:
This reduces the IRQ latency from O(nr_cgroups * nr_nohz_cpus) to O(nr_cgroups).
To the changelog of patch #1 ?
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