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Date: Thu, 19 Feb 2026 12:29:11 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	K Prateek Nayak <kprateek.nayak@amd.com>,
	"Gautham R . Shenoy" <gautham.shenoy@amd.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Chen Yu <yu.c.chen@intel.com>, Juri Lelli <juri.lelli@redhat.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
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	Valentin Schneider <vschneid@redhat.com>,
	Madadi Vineeth Reddy <vineethr@linux.ibm.com>,
	Hillf Danton <hdanton@sina.com>,
	Shrikanth Hegde <sshegde@linux.ibm.com>,
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	Aaron Lu <ziqianlu@bytedance.com>, Tim Chen <tim.c.chen@intel.com>,
	Josh Don <joshdon@google.com>, Gavin Guo <gavinguo@igalia.com>,
	Qais Yousef <qyousef@layalina.io>,
	Libo Chen <libchen@purestorage.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 03/21] sched/cache: Introduce helper functions to
 enforce LLC migration policy
Message-ID: <20260219112911.GF1395266@noisy.programming.kicks-ass.net>
References: <cover.1770760558.git.tim.c.chen@linux.intel.com>
 <7475922f6020abe5d458a136b0c88fe24e823091.1770760558.git.tim.c.chen@linux.intel.com>
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In-Reply-To: <7475922f6020abe5d458a136b0c88fe24e823091.1770760558.git.tim.c.chen@linux.intel.com>

On Tue, Feb 10, 2026 at 02:18:43PM -0800, Tim Chen wrote:

> +/*
> + * The margin used when comparing utilization.
> + * is 'util1' noticeably greater than 'util2'
> + * Derived from capacity_greater().
> + * Bias is in perentage.
> + */
> +/* Allows dst util to be bigger than src util by up to bias percent */
> +#define util_greater(util1, util2) \
> +	((util1) * 100 > (util2) * 120)

> + * 20% is the utilization imbalance percentage to decide
> + * if the preferred LLC is busier than the non-preferred LLC.
> + * 20 is a little higher than the LLC domain's imbalance_pct
> + * 17. The hysteresis is used to avoid task bouncing between the
> + * preferred LLC and the non-preferred LLC.

So not saying this needs changing now, but consider that imbalance_pct
can be changed through debugfs. Do you want this 120 to be expressed in
terms of imbalance_pct rather than being hardcoded?

Anyway, let me read on..