linux-kernel - Re: [PATCH v1 05/31] x86/resctrl: Remove rdtgroup from update_cpu_closid

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Date: Mon, 8 Apr 2024 20:16:08 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, H Peter Anvin
	<hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	<shameerali.kolothum.thodi@...wei.com>, D Scott Phillips OS
	<scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
	<tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>, Dave
 Martin <dave.martin@....com>
Subject: Re: [PATCH v1 05/31] x86/resctrl: Remove rdtgroup from
 update_cpu_closid_rmid()

Hi James,

On 3/21/2024 9:50 AM, James Morse wrote:
> update_cpu_closid_rmid() takes a struct rdtgroup as an argument, which
> it uses to update the local CPUs default pqr values. This is a problem
> once the resctrl parts move out to /fs/, as the arch code cannot
> poke around inside struct rdtgroup.
> 
> Rename update_cpu_closid_rmid() as resctrl_arch_sync_cpus_defaults()
> to be used as the target of an IPI, and pass the effective CLOSID
> and RMID in a new struct.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 +++++++++++++++----
>  include/linux/resctrl.h                | 11 +++++++++++
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 5d2c1ce5b6b1..18f097fce51e 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -341,13 +341,13 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
>   * from update_closid_rmid() is protected against __switch_to() because
>   * preemption is disabled.
>   */
> -static void update_cpu_closid_rmid(void *info)
> +void resctrl_arch_sync_cpu_defaults(void *info)
>  {
> -	struct rdtgroup *r = info;
> +	struct resctrl_cpu_sync *r = info;
>  
>  	if (r) {
>  		this_cpu_write(pqr_state.default_closid, r->closid);
> -		this_cpu_write(pqr_state.default_rmid, r->mon.rmid);
> +		this_cpu_write(pqr_state.default_rmid, r->rmid);
>  	}
>  
>  	/*
> @@ -362,11 +362,22 @@ static void update_cpu_closid_rmid(void *info)
>   * Update the PGR_ASSOC MSR on all cpus in @cpu_mask,
>   *
>   * Per task closids/rmids must have been set up before calling this function.
> + * @r may be NULL.
>   */
>  static void
>  update_closid_rmid(const struct cpumask *cpu_mask, struct rdtgroup *r)
>  {
> -	on_each_cpu_mask(cpu_mask, update_cpu_closid_rmid, r, 1);
> +	struct resctrl_cpu_sync defaults;
> +	struct resctrl_cpu_sync *defaults_p = NULL;

Please maintain reverse fir order.

> +
> +	if (r) {
> +		defaults.closid = r->closid;
> +		defaults.rmid = r->mon.rmid;
> +		defaults_p = &defaults;
> +	}
> +
> +	on_each_cpu_mask(cpu_mask, resctrl_arch_sync_cpu_defaults, defaults_p,
> +			 1);
>  }
>  
>  static int cpus_mon_write(struct rdtgroup *rdtgrp, cpumask_var_t newmask,
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 6e87bc95f5ea..2b79e4159507 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -220,6 +220,17 @@ struct resctrl_schema {
>  	u32				num_closid;
>  };
>  
> +struct resctrl_cpu_sync {
> +	u32 closid;
> +	u32 rmid;
> +};
> +
> +/*
> + * Update and re-load this CPUs defaults. Called via IPI, takes a pointer to

"this CPU's defaults"?

> + * struct resctrl_cpu_sync, or NULL.
> + */

Updating the CPU's defaults is not the primary goal of this function and because
of that I do not think this should be the focus with the main goal (updating
RMID and CLOSID on CPU) ignored. Specifically, this function only updates
the defaults if *info is set but it _always_ ensures CPU is running with
appropriate CLOSID/RMID (which may or may not be from a CPU default).

I think resctrl_arch_sync_cpu_closid_rmid() may be more appropriate
and the comment needs to elaborate what the function does.

> +void resctrl_arch_sync_cpu_defaults(void *info);
> +
>  /* The number of closid supported by this resource regardless of CDP */
>  u32 resctrl_arch_get_num_closid(struct rdt_resource *r);
>  int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);

Reinette