linux-kernel - Re: [PATCH v1 01/31] x86/resctrl: Fix allocation of cleanest CLOSID on platforms with no monitors

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Message-ID: <8d1d39ca-60f0-47e9-a090-f630c6df19ae@intel.com>
Date: Tue, 9 Apr 2024 08:02:28 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: David Hildenbrand <david@...hat.com>, James Morse <james.morse@....com>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>
CC: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, H Peter Anvin
	<hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	<shameerali.kolothum.thodi@...wei.com>, D Scott Phillips OS
	<scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
	<tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	Rex Nie <rex.nie@...uarmicro.com>, Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v1 01/31] x86/resctrl: Fix allocation of cleanest CLOSID
 on platforms with no monitors

Hi David,

(Thank you very much for taking a look at these)

On 4/9/2024 1:05 AM, David Hildenbrand wrote:
> On 21.03.24 17:50, James Morse wrote:
>> commit 6eac36bb9eb0 ("x86/resctrl: Allocate the cleanest CLOSID by
>> searching closid_num_dirty_rmid") added a Kconfig option that causes
>> resctrl to search for the CLOSID with the fewest dirty cache lines when
>> creating a new control group. This depends on the values read from the
>> llc_occupancy counters.
>>
>> This support missed that some platforms may not have these counters.
>> This causes a NULL pointer dereference when creating a new control
>> group as the array was not allocated by dom_data_init().
>>
>> As this feature isn't necessary on platforms that don't have cache
>> occupancy monitors, add this to the check that occurs when a new
>> control group is allocated.
>>
>> The existing code is not selected by any upstream platform, it makes
>> no sense to backport this patch to stable.
>>
> 
> It's weird to not see RESCTRL_RMID_DEPENDS_ON_CLOSID appear in any Kconfig file.
> I guess it will all make sense once the refactoring is done :)

This is done later in this series where patch #29, "fs/resctrl: Add boiler
plate for external resctrl code", introduces it to fs/resctrl/Kconfig.

Reinette