linux-kernel - Re: [PATCH v2 2/4] Add enabling of the R3 MWAIT during boot for KNL

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Date:   Wed, 12 Oct 2016 10:21:08 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org
Cc:     bp@...e.de, linux-kernel@...r.kernel.org, lukasz.daniluk@...el.com,
        james.h.cownie@...el.com
Subject: Re: [PATCH v2 2/4] Add enabling of the R3 MWAIT during boot for KNL

On 10/12/2016 05:16 AM, Grzegorz Andrejczuk wrote:
> @@ -211,6 +219,25 @@ static void early_init_intel(struct cpuinfo_x86 *c)
>  	}
>  
>  	check_mpx_erratum(c);
> +
> +	/*
> +	* Setting ring 3 MONITOR/MWAIT for all threads
> +	* when CPU is Xeon Phi Family x200
> +	* This can be disabled with phir3mwait=disable cmdline switch.
> +	* We preserve the reserved values and set only 2nd bit.
> +	* Ref:
> +	* https://software.intel.com/en-us/blogs/2016/10/06/intel-xeon-phi-product-family-x200-knl-user-mode-ring-3-monitor-and-mwait
> +	*/
> +	if (c->x86 == 6 &&
> +	    c->x86_model == INTEL_FAM6_XEON_PHI_KNL &&
> +	    phir3mwait) {
> +		u64 prev;
> +
> +		rdmsrl(MSR_PHI_MISC_THD_FEATURE, prev);
> +		if ((prev & MSR_PHI_MISC_THD_FEATURE_R3MWAIT) == 0)
> +			wrmsrl(MSR_PHI_MISC_THD_FEATURE,
> +			       prev | MSR_PHI_MISC_THD_FEATURE_R3MWAIT);
> +	}
>  }

I'd really prefer that we put hunks like this into helpers just like the
nice check_mpx_erratum().  I know early_init_intel() looks a lot like
what you have here, but I think a little:

	probe_xeon_phi_mwait()

would be a lot nicer.

BTW, this hunk totally indicates how badly named 'phir3mwait' is.  Could
you please give it a sane name like 'phi_r3_mwait_disabled'?