linux-kernel - Re: [PATCH 5/5] sched/fair: narrow the sched_use_asym

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Date: Thu, 25 Jan 2024 16:06:09 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: kuiliang Shi <seakeel@...il.com>
Cc: Shrikanth Hegde <sshegde@...ux.ibm.com>, alexs@...nel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] sched/fair: narrow the sched_use_asym_prio checking
 scenario

On Thu, Jan 25, 2024 at 05:35:32PM +0800, kuiliang Shi wrote:
> 
> 
> On 1/23/24 4:47 PM, Shrikanth Hegde wrote:
> > 
> > 
> > On 1/17/24 2:27 PM, alexs@...nel.org wrote:
> >> From: Alex Shi <alexs@...nel.org>
> >>
> >> Current function doesn't match it's comments, in fact, core_idle
> >> checking is only meaningful with non-SMT.
> >> So make the function right.
> >>
> >> Signed-off-by: Alex Shi <alexs@...nel.org>
> >> To: Valentin Schneider <vschneid@...hat.com>
> >> To: Vincent Guittot <vincent.guittot@...aro.org>
> >> To: Peter Zijlstra <peterz@...radead.org>
> >> To: Ingo Molnar <mingo@...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 96163ab69ae0..0a321f639c79 100644
> >> --- a/kernel/sched/fair.c
> >> +++ b/kernel/sched/fair.c
> >> @@ -9741,8 +9741,8 @@ group_type group_classify(unsigned int imbalance_pct,
> >>   */
> >>  static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
> >>  {
> >> -	return (!sched_smt_active()) ||
> >> -		(sd->flags & SD_SHARE_CPUCAPACITY) || is_core_idle(cpu);
> >> +	return	(sd->flags & SD_SHARE_CPUCAPACITY) ||
> >> +		(!sched_smt_active() && is_core_idle(cpu));
> >>  }
> > 
> > This seems wrong. This would always return false for higher than SMT domains 
> > if smt is active. 
> > 
> 
> yes, thanks for point out.
> 
> > Was this meant to be sched_smt_active() && is_core_idle(cpu)? 
> 
> In theory, yes, it should like this. But I have no ASYM device to test. :(

This would not work with !SMT and asym_packing.

I can test your patches on asym_packing + SMT systems if you post a new
version.