lkml.org 
[lkml]   [2021]   [Feb]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/7 v4] move update blocked load outside newidle_balance
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 ?

\
 
 \ /
  Last update: 2021-02-24 18:43    [W:0.162 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site