linux-kernel - Re: [PATCH 07/19] sched/fair: Track LLC-preferred tasks per runqueue

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Message-ID: <60fb91a69466e84d2367c11a4f0dd38511788bcb.camel@linux.intel.com>
Date: Wed, 15 Oct 2025 13:03:37 -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 07/19] sched/fair: Track LLC-preferred tasks per runqueue

On Wed, 2025-10-15 at 14:05 +0200, Peter Zijlstra wrote:
> On Sat, Oct 11, 2025 at 11:24:44AM -0700, Tim Chen wrote:
> > @@ -3999,6 +4038,7 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >  		struct rq *rq = rq_of(cfs_rq);
> >  
> >  		account_numa_enqueue(rq, task_of(se));
> > +		account_llc_enqueue(rq, task_of(se));
> >  		list_add(&se->group_node, &rq->cfs_tasks);
> 
> Here and...
> 
> >  	}
> >  	cfs_rq->nr_queued++;
> > @@ -4010,9 +4050,14 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >  	update_load_sub(&cfs_rq->load, se->load.weight);
> >  	if (entity_is_task(se)) {
> >  		account_numa_dequeue(rq_of(cfs_rq), task_of(se));
> > +		account_llc_dequeue(rq_of(cfs_rq), task_of(se));
> 
> ... here, could you please check the compiler is doing CSE of task_of()?

Will consolidate those task_of(se). 

> 
> >  		list_del_init(&se->group_node);
> >  	}
> >  	cfs_rq->nr_queued--;
> > +
> > +	/* safeguard to clear the cache aware data */
> > +	if (!parent_entity(se) && !cfs_rq->nr_queued)
> > +		reset_llc_stats(rq_of(cfs_rq));
> 
> I'm confused -- why?

Was put here in early code development to make
sure things would not go haywire.  Will remove
them.  Probably some warning of having tasks
preferring some LLC when there're no task in queue
is more appropriate.

Tim