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

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Message-Id: <20260109144746.95feaf11e4214cc4895d4039@linux-foundation.org>
Date: Fri, 9 Jan 2026 14:47:46 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Radu Rendec <rrendec@...hat.com>
Cc: "Guo, Wangyang" <wangyang.guo@...el.com>, 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 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.