linux-kernel - Re: [PATCH 2/3] selftests/resctrl: Fix a division by zero error on Hygon

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Message-ID: <de1d4a58-cff3-46af-8cae-520373d89d73@intel.com>
Date: Thu, 4 Dec 2025 16:56:24 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Xiaochen Shen <shenxiaochen@...n-hieco.net>, <tony.luck@...el.com>,
	<bp@...en8.de>, <fenghuay@...dia.com>
CC: <babu.moger@....com>, <james.morse@....com>, <Dave.Martin@....com>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] selftests/resctrl: Fix a division by zero error on
 Hygon

Hi Xiaochen,

On 12/4/25 4:38 AM, Xiaochen Shen wrote:
> Commit
> 
>   a1cd99e700ec ("selftests/resctrl: Adjust effective L3 cache size with SNC enabled")
> 
> introduced the snc_nodes_per_l3_cache() function to detect the Intel
> Sub-NUMA Clustering (SNC) feature by comparing #CPUs in node0 with #CPUs
> sharing LLC with CPU0. The function was designed to return:
>   (1) >1: SNC mode is enabled.
>   (2)  1: SNC mode is not enabled or not supported.
> 
> However, on certain Hygon CPUs, #CPUs sharing LLC with CPU0 is actually
> less than #CPUs in node0. This results in snc_nodes_per_l3_cache()
> returning 0 (calculated as cache_cpus / node_cpus).
> 
> This leads to a division by zero error in get_cache_size():
>   *cache_size /= snc_nodes_per_l3_cache();
> 
> Causing the resctrl selftest to fail with:
>   "Floating point exception (core dumped)"
> 
> Fix the issue by ensuring snc_nodes_per_l3_cache() returns 1 when SNC
> mode is not supported on the platform.
> 
> Fixes: a1cd99e700ec ("selftests/resctrl: Adjust effective L3 cache size with SNC enabled")
> Signed-off-by: Xiaochen Shen <shenxiaochen@...n-hieco.net>
> ---

Could you please include Shuah Khan <shuah@...nel.org> and linux-kselftest@...r.kernel.org 
in resctrl selftest posts?

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette