linux-kernel - Re: [PATCH v23 06/19] x86/resctrl: Introduce snc_nodes_per_l3

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Message-ID: <CALPaoCihZZXJDYmjZJP8nXyiUh7CdLKkKDyaOwb1yRRXWxXrNQ@mail.gmail.com>
Date: Fri, 26 Jul 2024 12:13:02 -0700
From: Peter Newman <peternewman@...gle.com>
To: Tony Luck <tony.luck@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>, Reinette Chatre <reinette.chatre@...el.com>, 
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, James Morse <james.morse@....com>, 
	Babu Moger <babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, 
	Dave Martin <Dave.Martin@....com>, x86@...nel.org, linux-kernel@...r.kernel.org, 
	patches@...ts.linux.dev
Subject: Re: [PATCH v23 06/19] x86/resctrl: Introduce snc_nodes_per_l3_cache

Hi Tony,

On Fri, Jun 28, 2024 at 2:56 PM Tony Luck <tony.luck@...el.com> wrote:
> @@ -1022,8 +1066,8 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>         int ret;
>
>         resctrl_rmid_realloc_limit = boot_cpu_data.x86_cache_size * 1024;
> -       hw_res->mon_scale = boot_cpu_data.x86_cache_occ_scale;
> -       r->num_rmid = boot_cpu_data.x86_cache_max_rmid + 1;
> +       hw_res->mon_scale = boot_cpu_data.x86_cache_occ_scale / snc_nodes_per_l3_cache;
> +       r->num_rmid = (boot_cpu_data.x86_cache_max_rmid + 1) / snc_nodes_per_l3_cache;

I noticed that resctrl_arch_system_num_rmid_idx() still returns a
value based on the original, undivided x86_cache_max_rmid. In my local
testing, this resulted in the alloc_rmid() returning values too large
for the arch_mbm_-arrays.

Please take a look at the patch I shared[1] to try to address this.

Thanks!
-Peter

[1] https://lore.kernel.org/lkml/20240722204611.3549213-1-peternewman@google.com/