linux-kernel - Re: [-v2 PATCH 2/6] powernow-k8: Add core performance boost support

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Date:	Wed, 31 Mar 2010 08:35:47 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	davej@...hat.com, trenn@...e.de, linux@...inikbrodowski.net,
	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	cpufreq@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [-v2 PATCH 2/6] powernow-k8: Add core performance boost support

From: Andrew Morton <akpm@...ux-foundation.org>
Date: Tue, Mar 30, 2010 at 11:22:21PM -0400

> On Wed, 31 Mar 2010 08:13:43 +0200 Borislav Petkov <bp@...64.org> wrote:
> 
> > > > +static void _cpb_toggle_msrs(bool t)
> > > > +{
> > > > +	int cpu;
> > > > +
> > > > +	rdmsr_on_cpus(cpu_online_mask, MSR_K7_HWCR, msrs);
> > > > +
> > > > +	for_each_cpu(cpu, cpu_online_mask) {
> > > > +		struct msr *reg = per_cpu_ptr(msrs, cpu);
> > > > +		if (t)
> > > > +			reg->l &= ~BIT(25);
> > > > +		else
> > > > +			reg->l |= BIT(25);
> > > > +	}
> > > > +	wrmsr_on_cpus(cpu_online_mask, MSR_K7_HWCR, msrs);
> > > > +}
> > > 
> > > What prevents cpu_online_mask from changing while this is happening?
> > 
> > Frankly, nothing.
> 
> Sneak a get_online_cpus()/put_online_cpus() in there?

Yep, that'll make it safe wrt to accessing the mask. I'll also have to
check whether there are some cores missing before toggling the bit and
warn accordingly. Do you want a relative diff ontop of this patch or
should I redo the original one?

Thanks.

-- 
Regards/Gruss,
Boris.

--
Advanced Micro Devices, Inc.
Operating Systems Research Center
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