linux-kernel - Re: [PATCH v19 18/20] x86/resctrl: Enable RMID shared RMID mode on Sub-NUMA Cluster (SNC) systems

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Date: Thu, 30 May 2024 13:27:31 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, Maciej
 Wieczor-Retman <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v19 18/20] x86/resctrl: Enable RMID shared RMID mode on
 Sub-NUMA Cluster (SNC) systems

Hi Tony,

On 5/28/24 3:20 PM, Tony Luck wrote:
> There is an MSR which configures how RMIDs are distributed across SNC
> nodes. When SNC is enabled bit 0 of this MSR must be cleared.

Missing explanation why bit 0 of this MSR must be cleared.

> 
> Add an architecture specific hook into domain_add_cpu_mon() to call
> a function to set the MSR.

Can this explain more than what the code already tells us?

> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>   arch/x86/include/asm/msr-index.h       |  1 +
>   arch/x86/kernel/cpu/resctrl/internal.h |  2 ++
>   arch/x86/kernel/cpu/resctrl/core.c     |  2 ++
>   arch/x86/kernel/cpu/resctrl/monitor.c  | 26 ++++++++++++++++++++++++++
>   4 files changed, 31 insertions(+)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index e022e6eb766c..3cb8dd6311c3 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -1164,6 +1164,7 @@
>   #define MSR_IA32_QM_CTR			0xc8e
>   #define MSR_IA32_PQR_ASSOC		0xc8f
>   #define MSR_IA32_L3_CBM_BASE		0xc90
> +#define MSR_RMID_SNC_CONFIG		0xca0
>   #define MSR_IA32_L2_CBM_BASE		0xd10
>   #define MSR_IA32_MBA_THRTL_BASE		0xd50
>   
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 7957fc38b71c..08520321f5d0 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -532,6 +532,8 @@ static inline bool resctrl_arch_get_cdp_enabled(enum resctrl_res_level l)
>   
>   int resctrl_arch_set_cdp_enabled(enum resctrl_res_level l, bool enable);
>   
> +void arch_mon_domain_online(struct rdt_resource *r, struct rdt_mon_domain *d);

I expect that this function will be called from the already
architecture specific code so needing an architecture specific hook as the changelog
mentions does not seem appropriate.

Reinette