linux-kernel - Re: [PATCH v4 2/4] x86/phi: Add enabling of the R3MWAIT during boot

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Message-ID: <alpine.DEB.2.20.1610202105000.4938@nanos>
Date:   Thu, 20 Oct 2016 21:10:00 +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 v4 2/4] x86/phi: Add enabling of the R3MWAIT during
 boot

On Tue, 18 Oct 2016, Grzegorz Andrejczuk wrote:
> +static void probe_xeon_phi_r3mwait(struct cpuinfo_x86 *c)
> +{
> +	if (phi_r3mwait_disabled)
> +		return;

So you return when the command line option to disable the feature was
given. That's not really a good choice if the feature is already enabled
due to BIOS featuritis. This can also happen when you kexec from a enabled
kernel into one which has the command line option set.

You really should make sure that the command line option results in
disabling the feature no matter what.

Thanks,

	tglx