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

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 26 Mar 2010 14:39:56 +0100
Borislav Petkov <bp@amd64.org> wrote:

> From: Borislav Petkov <borislav.petkov@amd.com>
> 
> Starting with F10h, revE, AMD processors add support for a dynamic
> core boosting feature called Core Performance Boost. When a specific
> condition is present, a subset of the cores on a system are boosted
> beyond their P0 operating frequency to speed up the performance of
> single-threaded applications.
> 
> In the normal case, the system comes out of reset with core boosting
> enabled. This patch adds a sysfs knob with which core boosting can be
> switched on or off for benchmarking purposes.
> 
> While at it, cleanup the driver init codepath and update copyrights.
> 
> ...
>
> +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?

> @@ -1422,15 +1490,34 @@ static int __cpuinit powernowk8_init(void)
>  			supported_cpus++;
>  	}
>  
> -	if (supported_cpus == num_online_cpus()) {
> -		printk(KERN_INFO PFX "Found %d %s "
> -			"processors (%d cpu cores) (" VERSION ")\n",
> -			num_online_nodes(),
> -			boot_cpu_data.x86_model_id, supported_cpus);
> -		return cpufreq_register_driver(&cpufreq_amd64_driver);
> +	if (supported_cpus != num_online_cpus())
> +		return -ENODEV;
> +
> +	printk(KERN_INFO PFX "Found %d %s (%d cpu cores) (" VERSION ")\n",
> +		num_online_nodes(), boot_cpu_data.x86_model_id, supported_cpus);
> +
> +	if (boot_cpu_has(X86_FEATURE_CPB)) {
> +
> +		cpb_capable = true;
> +
> +		msrs = msrs_alloc();
> +		if (!msrs) {
> +			printk(KERN_ERR "%s: Error allocating msrs!\n", __func__);
> +			return -ENOMEM;
> +		}
> +
> +		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);
> +			cpb_enabled |= !(!!(reg->l & BIT(25)));
> +		}

Ditto.

I assume these changes get applied to new CPUs as they come online?

> ...