linux-kernel - Re: [PATCH 09/19] sched/fair: Count tasks prefering each LLC in a sched group

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Message-ID: <c81fd23152d07775dc0482353a01ca6b56f20f85.camel@linux.intel.com>
Date: Mon, 27 Oct 2025 16:19:17 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: K Prateek Nayak <kprateek.nayak@....com>, Peter Zijlstra	
 <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "Gautham R .
 Shenoy"	 <gautham.shenoy@....com>
Cc: 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 09/19] sched/fair: Count tasks prefering each LLC in a
 sched group

On Mon, 2025-10-27 at 14:03 +0530, K Prateek Nayak wrote:
> Hello Tim,
> 
> On 10/11/2025 11:54 PM, Tim Chen wrote:
> > +#ifdef CONFIG_SCHED_CACHE
> > +		if (sched_cache_enabled()) {
> > +			int j;
> > +
> > +			for (j = 0; j < max_llcs; ++j)
> > +				sgs->nr_pref_llc[j] += rq->nr_pref_llc[j];
> > +		}
> > +#endif
> 
> If I'm not mistaken, we only compare
> "sds->nr_pref_llc[llc_idx(env->dst_cpu)]"
> and the destination LLC is always fixes. Do we need to aggregate the
> data for all the LLCs? Is a single "nr_pref_llc_dest" enough?

Yes. Only the nr_pref_llc entry corresponding to the destination
LLC is going to be used later to find either the LLC or run queue
to be chosen for balancing.  We can skip accounting for the other LLCs and save
some memory here.

Tim

> 
> >  		/*
> >  		 * No need to call idle_cpu() if nr_running is not 0
> >  		 */