linux-kernel - Re: [PATCH v11 01/13] x86/resctrl: Replace smp_call_function_many() with on_each_cpu

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Date:   Mon, 9 Jan 2023 23:26:56 +0000
From:   Ashok Raj <ashok_raj@...ux.intel.com>
To:     Babu Moger <babu.moger@....com>
Cc:     corbet@....net, reinette.chatre@...el.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, fenghua.yu@...el.com,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        paulmck@...nel.org, akpm@...ux-foundation.org,
        quic_neeraju@...cinc.com, rdunlap@...radead.org,
        damien.lemoal@...nsource.wdc.com, songmuchun@...edance.com,
        peterz@...radead.org, jpoimboe@...nel.org, pbonzini@...hat.com,
        chang.seok.bae@...el.com, pawan.kumar.gupta@...ux.intel.com,
        jmattson@...gle.com, daniel.sneddon@...ux.intel.com,
        sandipan.das@....com, tony.luck@...el.com, james.morse@....com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        bagasdotme@...il.com, eranian@...gle.com,
        christophe.leroy@...roup.eu, jarkko@...nel.org,
        adrian.hunter@...el.com, quic_jiles@...cinc.com,
        peternewman@...gle.com, Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v11 01/13] x86/resctrl: Replace smp_call_function_many()
 with on_each_cpu_mask()

On Mon, Jan 09, 2023 at 10:43:53AM -0600, Babu Moger wrote:
> on_each_cpu_mask() runs the function on each CPU specified by cpumask,
> which may include the local processor.
> 
> Replace smp_call_function_many() with on_each_cpu_mask() to simplify
> the code.
> 
> Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 11 +++------
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 29 +++++++----------------
>  2 files changed, 11 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index 1df0e3262bca..7eece3d2d0c3 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -310,7 +310,6 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
>  	enum resctrl_conf_type t;
>  	cpumask_var_t cpu_mask;
>  	struct rdt_domain *d;
> -	int cpu;
>  	u32 idx;
>  
>  	if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
> @@ -341,13 +340,9 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
>  
>  	if (cpumask_empty(cpu_mask))
>  		goto done;
> -	cpu = get_cpu();
> -	/* Update resource control msr on this CPU if it's in cpu_mask. */
> -	if (cpumask_test_cpu(cpu, cpu_mask))
> -		rdt_ctrl_update(&msr_param);
> -	/* Update resource control msr on other CPUs. */
> -	smp_call_function_many(cpu_mask, rdt_ctrl_update, &msr_param, 1);
> -	put_cpu();
> +
> +	/* Update resource control msr on all the CPUs. */
> +	on_each_cpu_mask(cpu_mask, rdt_ctrl_update, &msr_param, 1);

Do you require these updates to done immediately via an IPI? or can they be
done bit lazy via schedule_on_each_cpu()? 

Cheers,
Ashok