From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99423192590
	for <linux-kernel@vger.kernel.org>; Thu,  9 Apr 2026 23:00:36 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1775775640; cv=none; b=Tm+Yg3eNBg8JuAouPlVmEDxVjdsYHRqGFQOYx1qZaOm0wis7ge8EPe5s7OLphOxWTTSmH99S0Sg2P/E+WSw9oIqyiC1OAffMtIQMbCqY8aeXzJ1syW+Cq2rveCQ5xszNKXQyltIdZPzygwdjsSQm1NKA7AJHg+Nj19zp6Umqsks=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1775775640; c=relaxed/simple;
	bh=woZfiYiKiTfhnNRVP1VmsGEh/mozRg/SLFuR2AiVbxU=;
	h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version:
	 Content-Type:Content-Disposition:In-Reply-To; b=PfDU7UsQOe8HGfoVby2/JuWrswJ5ZVAmgs49Eh8hijDHYkY6e9My7QqCKu8uxO21Mbs7gW4GUlH73izTmgsyTQ2tHVNl5xVNDJi5zXkm9QIbEZoNKXEii7+S4m7t8Tm/c7YoEurisZZ8lLSsEChOdLKFDuE1nQn2hQKcwYcu2sU=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=QEiggTpe; arc=none smtp.client-ip=90.155.92.199
Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org
Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org
Authentication-Results: smtp.subspace.kernel.org;
	dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="QEiggTpe"
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
	d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version:
	References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:
	Content-Transfer-Encoding:Content-ID:Content-Description;
	bh=+1OD1OHjO3F3EicS22OQJ9UZwzuQYvj4594nPouI6No=; b=QEiggTpe+kpo3RofVsaHA0+XUT
	yfuC5rOvCSs2oHH4Lb5Oc7vfkO3AnRo6AmA8y9UduroEzUvn4qsjGYWeFX/LszjuBZxFer6Wf3t/M
	05LaZU5CyKzDf/UJLVUAgc8zPMefZXF1v5vHHIca2FSKuoS3T0Ct+usofxYcuguFCWAD7m+DWdU1G
	e94OD8r/qDdTRZqi3pkjYU9dPclt5uVg7tRlj8pMlnWkNEScR6766H4JTbSHgcPJKenvEcpjCv4kz
	GrWe35m3dqiPdbvICMRgDracC5DXH52QbOlMtjP9FhMd8QwW5vQE/LFBFQsk3DtRrQ7vYrVtdIXJ/
	x8t/Rjeg==;
Received: from 2001-1c00-8d85-4b00-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:4b00:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net)
	by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux))
	id 1wAyM1-0000000CXuV-3ovQ;
	Thu, 09 Apr 2026 23:00:06 +0000
Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000)
	id 4B75F300583; Fri, 10 Apr 2026 01:00:04 +0200 (CEST)
Date: Fri, 10 Apr 2026 01:00:04 +0200
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>,
	Juri Lelli <juri.lelli@redhat.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Valentin Schneider <vschneid@redhat.com>,
	Madadi Vineeth Reddy <vineethr@linux.ibm.com>,
	Hillf Danton <hdanton@sina.com>,
	Shrikanth Hegde <sshegde@linux.ibm.com>,
	Jianyong Wu <jianyong.wu@outlook.com>,
	Yangyu Chen <cyy@cyyself.name>,
	Tingyin Duan <tingyin.duan@gmail.com>,
	Vern Hao <vernhao@tencent.com>, Vern Hao <haoxing990@gmail.com>,
	Len Brown <len.brown@intel.com>, Aubrey Li <aubrey.li@intel.com>,
	Zhao Liu <zhao1.liu@intel.com>, Chen Yu <yu.chen.surf@gmail.com>,
	Chen Yu <yu.c.chen@intel.com>,
	Adam Li <adamli@os.amperecomputing.com>,
	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 v4 01/22] sched/cache: Introduce infrastructure for
 cache-aware load balancing
Message-ID: <20260409230004.GV2872@noisy.programming.kicks-ass.net>
References: <cover.1775065312.git.tim.c.chen@linux.intel.com>
 <6269a53221b9439b9ca00d18a9d1946fb64d8cff.1775065312.git.tim.c.chen@linux.intel.com>
 <20260409124110.GA3126523@noisy.programming.kicks-ass.net>
 <71b4ddab042b805a225eef92b0a9404b20aa2b98.camel@linux.intel.com>
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <71b4ddab042b805a225eef92b0a9404b20aa2b98.camel@linux.intel.com>

On Thu, Apr 09, 2026 at 12:21:58PM -0700, Tim Chen wrote:

> > > +	    get_nr_threads(p) <= 1) {
> > 
> > And this, I just noticed this, why are we excluding tasks with one
> > thread? The comment just states we are (doh), but utterly fails to
> > explain why.
> 
> The thought was that for a single thread, we will tend to place it
> in same LLC as it was previously running with cache hot.  Incurring
> the added cost of tracking its residency in LLC is uneeded.

Not sure -- the moment it gets migrated away, it will stay away. There
is no force to pull it back, while with cache aware it will try and come
back for a short while -- until it's build an occupancy on the new llc.

Anyway, if you want to do this, it needs to be a separate patch.