linux-kernel - Re: [PATCH 11/19] sched/fair: Identify busiest sched

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Message-ID: <b34b4763a07d3d2043ebd2dc968802179ad6efa8.camel@linux.intel.com>
Date: Wed, 15 Oct 2025 14:18:08 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, K Prateek Nayak
 <kprateek.nayak@....com>,  "Gautham R . Shenoy" <gautham.shenoy@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>, Juri Lelli	
 <juri.lelli@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>,  Valentin Schneider	 <vschneid@...hat.com>,
 Madadi Vineeth Reddy <vineethr@...ux.ibm.com>, Hillf Danton
 <hdanton@...a.com>, Shrikanth Hegde <sshegde@...ux.ibm.com>, Jianyong Wu	
 <jianyong.wu@...look.com>, Yangyu Chen <cyy@...self.name>, Tingyin Duan	
 <tingyin.duan@...il.com>, Vern Hao <vernhao@...cent.com>, Len Brown	
 <len.brown@...el.com>, Aubrey Li <aubrey.li@...el.com>, Zhao Liu	
 <zhao1.liu@...el.com>, Chen Yu <yu.chen.surf@...il.com>, Chen Yu	
 <yu.c.chen@...el.com>, Libo Chen <libo.chen@...cle.com>, Adam Li	
 <adamli@...amperecomputing.com>, Tim Chen <tim.c.chen@...el.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/19] sched/fair: Identify busiest sched_group for
 LLC-aware load balancing

On Wed, 2025-10-15 at 17:24 +0200, Peter Zijlstra wrote:
> On Sat, Oct 11, 2025 at 11:24:48AM -0700, Tim Chen wrote:
> 
> > @@ -11035,6 +11059,17 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> >  	     sds->local_stat.group_type != group_has_spare))
> >  		return false;
> >  
> > +	/* deal with prefer LLC load balance, if failed, fall into normal load balance */
> > +	if (update_llc_busiest(env, busiest, sgs))
> > +		return true;
> > +
> > +	/*
> > +	 * If the busiest group has tasks with LLC preference,
> > +	 * skip normal load balance.
> > +	 */
> > +	if (busiest->group_llc_balance)
> > +		return false;
> > +
> >  	if (sgs->group_type > busiest->group_type)
> >  		return true;
> 
> This feels weird.. should we really override things like group_imbalance
> or group_misfit_task ?

Probably make sense to move the group_llc_balance priority to be lower than group_imblanace
and group_misfit_task. Will update accordingly.

Tim