linux-kernel - Re: [PATCH v12 7/8] x86/resctrl: Sub NUMA Cluster detection and enable

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Date:   Thu, 30 Nov 2023 18:08:29 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Tony Luck <tony.luck@...el.com>
CC:     Fam Zheng <fam@...hon.net>, Fenghua Yu <fenghua.yu@...el.com>,
        "Peter Newman" <peternewman@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, <x86@...nel.org>,
        Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Babu Moger <babu.moger@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <patches@...ts.linux.dev>,
        Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v12 7/8] x86/resctrl: Sub NUMA Cluster detection and
 enable

Hi Tony,

On 11/30/2023 4:37 PM, Tony Luck wrote:
> On Thu, Nov 30, 2023 at 03:40:52PM -0800, Reinette Chatre wrote:
>> Hi Tony,
>>
>> On 11/30/2023 2:43 PM, Tony Luck wrote:
>>> On Thu, Nov 30, 2023 at 01:47:10PM -0800, Reinette Chatre wrote:

>> for something that does not change while not holding the hotplug lock. Reading its
>> description more closely also makes me wonder if the later
>> 	num_online_cpus() != num_present_cpus()
>> should also maybe be 
>> 	num_online_cpus() != num_possible_cpus() ?
>> It seems to more closely match the intention.
> 
> This seems problematic. On a system that does support physical CPU
> hotplug num_possible_cpus() may be some very large number. Reserving
> space for CPUs that can be added later. None of those CPUs can be online
> (obviously!). So this test would fail on such a system.

Thank you for clarifying. It was not obvious to me how these bitmaps are
different with physical hotplug. 

Reinette