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Message-ID: <f86710be-1561-49a5-87ee-b3ce71fc9dc4@intel.com>
Date:   Thu, 30 Nov 2023 18:08:29 -0800
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Subject: Re: [PATCH v12 7/8] x86/resctrl: Sub NUMA Cluster detection and
 enable
Content-Language: en-US
To:     Tony Luck <tony.luck@intel.com>
CC:     Fam Zheng <fam@euphon.net>, Fenghua Yu <fenghua.yu@intel.com>,
        "Peter Newman" <peternewman@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <skhan@linuxfoundation.org>, <x86@kernel.org>,
        Shaopeng Tan <tan.shaopeng@fujitsu.com>,
        James Morse <james.morse@arm.com>,
        Jamie Iles <quic_jiles@quicinc.com>,
        Babu Moger <babu.moger@amd.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-doc@vger.kernel.org>,
        <patches@lists.linux.dev>,
        Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
References: <20231109230915.73600-1-tony.luck@intel.com>
 <20231130003418.89964-1-tony.luck@intel.com>
 <20231130003418.89964-8-tony.luck@intel.com> <ZWjOBw0Ygyw226Cc@dell>
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 <1c1a16a5-f235-4179-9d0f-1556e11d9c11@intel.com>
 <ZWkQBwwtSae4nGgH@agluck-desk3>
 <5078f930-e56e-45b5-9df3-99e88c0858dd@intel.com>
 <ZWkqv+egQuph03Bm@agluck-desk3>
From:   Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <ZWkqv+egQuph03Bm@agluck-desk3>
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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