linux-kernel - Re: [PATCH 13/21] x86/intel_rdt/cqm: Add cpus file support

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Date:   Sun, 2 Jul 2017 13:11:57 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com,
        peterz@...radead.org, ravi.v.shankar@...el.com,
        vikas.shivappa@...el.com, tony.luck@...el.com,
        fenghua.yu@...el.com, andi.kleen@...el.com
Subject: Re: [PATCH 13/21] x86/intel_rdt/cqm: Add cpus file support

On Mon, 26 Jun 2017, Vikas Shivappa wrote:
> diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
> index fdf3654..fec8ba9 100644
> --- a/arch/x86/kernel/cpu/intel_rdt.h
> +++ b/arch/x86/kernel/cpu/intel_rdt.h
> @@ -37,6 +37,8 @@ struct mon_evt {
>  extern bool rdt_alloc_enabled;
>  extern int rdt_mon_features;
>  
> +DECLARE_PER_CPU_READ_MOSTLY(int, cpu_rmid);

u32

>  
> +DEFINE_PER_CPU_READ_MOSTLY(int, cpu_rmid);
>  static inline struct rmid_entry *__rmid_entry(u32 rmid)

Bah. Please add a new line between the DEFINE... and the function.

But that whole thing is wrong. The per cpu default closid and rmid want to
be in a single place, not in two distinct per cpu variables.

struct rdt_cpu_default {
       u32	rmid;
       u32	closid;
};

DEFINE_PER_CPU_READ_MOSTLY(struct rdt_cpu_default, rdt_cpu_default);

or something like this. That way it's guaranteed that the context switch
code touches a single cache line for the per cpu defaults.

Thanks,

	tglx