linux-kernel - Re: [PATCH 5/9] sched/balancing: Fix comments (trying to) refer to NOHZ_BALANCE

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Date: Fri, 8 Mar 2024 11:11:51 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: linux-kernel@...r.kernel.org, Shrikanth Hegde <sshegde@...ux.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH 5/9] sched/balancing: Fix comments (trying to) refer to
 NOHZ_BALANCE_KICK


* Vincent Guittot <vincent.guittot@...aro.org> wrote:

> On Mon, 4 Mar 2024 at 10:48, Ingo Molnar <mingo@...nel.org> wrote:
> >
> > Fix two typos:
> >
> >  - There's no such thing as 'nohz_balancing_kick', the
> >    flag is named 'BALANCE' and is capitalized:  NOHZ_BALANCE_KICK.
> >
> >  - Likewise there's no such thing as a 'pending nohz_balance_kick'
> >    either, the NOHZ_BALANCE_KICK flag is all upper-case.
> >
> > Signed-off-by: Ingo Molnar <mingo@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Vincent Guittot <vincent.guittot@...aro.org>
> > Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > Cc: Valentin Schneider <vschneid@...hat.com>
> > ---
> >  kernel/sched/fair.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 934ace69eb30..4c46bffb6a7a 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -12410,14 +12410,14 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
> >
> >  /*
> >   * run_rebalance_domains is triggered when needed from the scheduler tick.
> > - * Also triggered for nohz idle balancing (with nohz_balancing_kick set).
> 
> I think it should be nohz_balancer_kick() instead of nohz_balancing_kick
> 
> 
> > + * Also triggered for NOHZ idle balancing (with NOHZ_BALANCE_KICK set).
> 
> In fact, this can be triggered even without NOHZ_BALANCE_KICK. Any of
> the below can trigger this
>   - NOHZ_BALANCE_KICK
>   - NOHZ_STATS_KICK
>   - NOHZ_NEXT_KICK

Yeah, indeed any of the flags in NOHZ_KICK_MASK can trigger nohz_csd and 
indirect the balancing softirq - so I changed the text to:

  /*                      
   * This softirq may be triggered from the scheduler tick, or by
   * any of the flags in NOHZ_KICK_MASK: NOHZ_BALANCE_KICK,
   * NOHZ_STATS_KICK or NOHZ_NEXT_KICK.
   */
  static __latent_entropy void run_rebalance_domains(struct softirq_action *h)

Thanks,

	Ingo