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

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Date: Tue, 9 Apr 2024 17:06:03 +0200
From: David Hildenbrand <david@...hat.com>
To: Reinette Chatre <reinette.chatre@...el.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

On 09.04.24 17:02, Reinette Chatre wrote:
> Hi David,
> 

Hi,

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

I'm planning on reviewing more; as most of resctrl is code I haven't 
really read before, I'm not able to make progress as fast as I normally 
would in core-MM ... :)

> 
> 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.

Oh, already in this series, great!

-- 
Cheers,

David / dhildenb