linux-kernel - Re: [PATCH] lib/group_cpus: make group CPU cluster aware

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Message-ID: <a361e213-1cf2-43be-9dd4-4f73a71906af@intel.com>
Date: Tue, 13 Jan 2026 10:37:39 +0800
From: "Guo, Wangyang" <wangyang.guo@...el.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
 Radu Rendec <rrendec@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
 Tianyou Li <tianyou.li@...el.com>, Tim Chen <tim.c.chen@...ux.intel.com>,
 Dan Liang <dan.liang@...el.com>
Subject: Re: [PATCH] lib/group_cpus: make group CPU cluster aware

On 1/10/2026 6:47 AM, Andrew Morton wrote:
> On Fri, 09 Jan 2026 14:13:32 -0500 Radu Rendec <rrendec@...hat.com> wrote:
> 
>>>>> This patch improves IRQ affinity by grouping CPUs by cluster within each
>>>>> NUMA domain, ensuring better locality between CPUs and their assigned
>>>>> NVMe IRQs.
>>>>>
>>>>> Reviewed-by: Tianyou Li <tianyou.li@...el.com>
>>>>> Reviewed-by: Tim Chen <tim.c.chen@...ux.intel.com>
>>>>> Tested-by: Dan Liang <dan.liang@...el.com>
>>>>> Signed-off-by: Wangyang Guo <wangyang.guo@...el.com>
>>>>
>>>> Patch hasn't attracted additional review so I'll queue this version for
>>>> some testing in mm.git's mm-nonmm-unstable branch.  I'll add a
>>>> note-to-self that a changelog addition is desirable.
>>>
>>>
>>> Thanks a lot for your time and support! Please let me know if you have
>>> any further comments or guidance. Any feedback would be appreciated.
>>
>> With this patch applied, I see a weird issue in a qemu x86_64 vm if I
>> start it with a higher number of max CPUs than active CPUs, for example
>> `-smp 4,maxcpus=8` on the qemu command line.
>>
>> What I see is the `while (1)` loop in alloc_cluster_groups() spinning
>> forever. Removing the `maxcpus=8` from the qemu command line fixes the
>> issue but so does reverting the patch :)
> 
> Great, thanks, I'll drop the patch.
> 
> I have notes here that an updated version is expected anyway.  Perhaps
> due to planned changelog updates.  And perhaps hopes for additional
> info regarding the runtime effects of the change.

This issue has been fixed and change log also updated as below:
https://lore.kernel.org/all/20260113022958.3379650-1-wangyang.guo@intel.com/T/#u

BR
Wangyang