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

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Message-ID: <da1d6b4e-038c-48dc-830d-5eadb3ac943f@intel.com>
Date: Tue, 18 Nov 2025 14:29:20 +0800
From: "Guo, Wangyang" <wangyang.guo@...el.com>
To: Ming Lei <ming.lei@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Thomas Gleixner <tglx@...utronix.de>, Keith Busch <kbusch@...nel.org>,
 Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
 Sagi Grimberg <sagi@...mberg.me>, linux-kernel@...r.kernel.org,
 linux-nvme@...ts.infradead.org, virtualization@...ts.linux-foundation.org,
 linux-block@...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 RESEND] lib/group_cpus: make group CPU cluster aware

On 11/13/2025 9:38 AM, Ming Lei wrote:
> On Wed, Nov 12, 2025 at 11:02:47AM +0800, Guo, Wangyang wrote:
>> On 11/11/2025 8:08 PM, Ming Lei wrote:
>>> On Tue, Nov 11, 2025 at 01:31:04PM +0800, Guo, Wangyang wrote:
>>> They still should share same L3 cache, and cpus_share_cache() should be
>>> true when the IO completes on the CPU which belong to different L2 with the
>>> submission CPU, and remote completion via IPI won't be triggered.
>> Yes, remote IPI not triggered.
> 
> OK, in my test on AMD zen4, NVMe performance can be dropped to 1/2 - 1/3 if
> remote IPI is triggered in case of crossing L3, which is understandable.
> 
> I will check if topo cluster can cover L3, if yes, the patch still can be
> simplified a lot by introducing sub-node spread by changing build_node_to_cpumask()
> and adding nr_sub_nodes.

Do you mean using cluster as "NUMA" nodes to spread CPU, instead of two 
level NUMA-cluster spreading?

BR
Wangyang