linux-kernel - Re: [PATCH v4 3/4] sched/fair: Rework sched_use_asym_prio() and sched_asym

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Date: Fri, 9 Feb 2024 17:16:43 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: kuiliang Shi <seakeel@...il.com>
Cc: 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>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org, yangyicong@...ilicon.com
Subject: Re: [PATCH v4 3/4] sched/fair: Rework sched_use_asym_prio() and
 sched_asym_prefer()

On Fri, Feb 09, 2024 at 07:08:52PM +0800, kuiliang Shi wrote:
> 
> 
> On 2/9/24 10:47 AM, Ricardo Neri wrote:
> > On Wed, Feb 07, 2024 at 11:47:03AM +0800, alexs@...nel.org wrote:
> >> From: Alex Shi <alexs@...nel.org>
> >>
> >> sched_use_asym_prio() sched_asym_prefer() are used together in various
> > 
> > s/prio() sched/prio() and sched/
> 
> Will take it, Thanks!
> 
> > 
> >> places. Consolidate them into a single function sched_asym().
> >>
> >> The existing sched_group_asym() is only used when collecting statistics
> >> of a scheduling group. Rename it as sched_group_asym().
> >> This makes the code easier to read. No functional changes.
> >>
> >> Signed-off-by: Alex Shi <alexs@...nel.org>
> >> To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> >> 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 | 37 ++++++++++++++++++++-----------------
> >>  1 file changed, 20 insertions(+), 17 deletions(-)
> >>
> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >> index 607dc310b355..942b6358f683 100644
> >> --- a/kernel/sched/fair.c
> >> +++ b/kernel/sched/fair.c
> >> @@ -9746,8 +9746,18 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
> >>  	return sd->flags & SD_SHARE_CPUCAPACITY || is_core_idle(cpu);
> >>  }
> >>  
> >> +static inline bool sched_asym(struct sched_domain *sd, int dst_cpu, int src_cpu)
> >> +{
> >> +	/*
> >> +	 * First check if @dst_cpu can do asym_packing load balance. Only do it
> >> +	 * if it has higher priority than @src_cpu.
> >> +	 */
> >> +	return sched_use_asym_prio(sd, dst_cpu) &&
> >> +		sched_asym_prefer(dst_cpu, src_cpu);
> >> +}
> >> +
> >>  /**
> >> - * sched_asym - Check if the destination CPU can do asym_packing load balance
> >> + * sched_group_asym - Check if the destination CPU can do asym_packing balance
> >>   * @env:	The load balancing environment
> >>   * @sgs:	Load-balancing statistics of the candidate busiest group
> >>   * @group:	The candidate busiest group
> > 
> > After renaming and changing this function now its documentation has become
> > obsolete. Can you update it?
> 
> Since the function sched_use_asym_prio() and sched_asym_prefer() both give detailed comments for their actions, as long as this function does, could we just remove the bit obsolete comments here?
> 
> 
> @@ -9765,14 +9765,6 @@ static inline bool sched_asym(struct sched_domain *sd, int dst_cpu, int src_cpu)
>   * @env::dst_cpu can do asym_packing if it has higher priority than the
>   * preferred CPU of @group.
>   *
> - * SMT is a special case. If we are balancing load between cores, @env::dst_cpu
> - * can do asym_packing balance only if all its SMT siblings are idle. Also, it
> - * can only do it if @group is an SMT group and has exactly on busy CPU. Larger
> - * imbalances in the number of CPUS are dealt with in find_busiest_group().
> - *
> - * If we are balancing load within an SMT core, or at PKG domain level, always
> - * proceed.
> - *
>   * Return: true if @env::dst_cpu can do with asym_packing load balance. False
>   * otherwise.

Fine with me.

With this change,
Reviewed-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>

Tested on Alder Lake and Meteor Lake, which use asym_packing.

Tested-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> >