linux-kernel - Re: [PATCH v3 2/4] Add enabling of the R3 MWAIT during boot for KNL

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Date:   Thu, 13 Oct 2016 17:32:28 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>
cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org, bp@...e.de,
        dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org,
        lukasz.daniluk@...el.com, james.h.cownie@...el.com,
        jacob.jun.pan@...el.com
Subject: Re: [PATCH v3 2/4] Add enabling of the R3 MWAIT during boot for
 KNL

On Thu, 13 Oct 2016, Grzegorz Andrejczuk wrote:
>  
> +static int phi_r3mwait_disabled;

__read_mostly please.

> +
>  /*
>   * Just in case our CPU detection goes bad, or you have a weird system,
>   * allow a way to override the automatic disabling of MPX.
> @@ -61,6 +63,34 @@ void check_mpx_erratum(struct cpuinfo_x86 *c)
>  	}
>  }
>  
> +static int __init phir3mwait_disable(char *__unused)
> +{
> +	phi_r3mwait_disabled = 1;
> +
> +	return 1;
> +}
> +__setup("phir3mwait=disable", phir3mwait_disable);

This needs proper documentation in Documentation/kernel-parameters.txt

> +static void __init probe_xeon_phi_r3mwait(struct cpuinfo_x86 *c)
> +{
> +	if (phi_r3mwait_disabled)
> +		return;
> +
> +	/*
> +	* Setting ring 3 MONITOR/MWAIT for all threads
> +	* when CPU is Xeon Phi Family x200


> +	* This can be disabled with phir3mwait=disable cmdline switch.

And why is this information useful in this comment? 

> +	* We preserve the reserved values and set only 2nd bit.

This last sentence does not make any sense at all.

Thanks,

	tglx