linux-kernel - Re: [PATCH v2: kvm 2/4] Kill the confusing tsc_ref_khz and ref

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Message-ID: <4AC1C557.2050002@redhat.com>
Date:	Tue, 29 Sep 2009 10:29:11 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Zachary Amsden <zamsden@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v2: kvm 2/4] Kill the confusing tsc_ref_khz and ref_freq
 variables.

On 09/29/2009 06:04 AM, Zachary Amsden wrote:
> They are globals, not clearly protected by any ordering or locking, and
> vulnerable to various startup races.
>
> Instead, for variable TSC machines, register the cpufreq notifier and get
> the TSC frequency directly from the cpufreq machinery.  Not only is it
> always right, it is also perfectly accurate, as no error prone measurement
> is required.
>
> On such machines, when a new CPU online is brought online, it isn't clear what
> frequency it will start with, and it may not correspond to the reference, thus
> in hardware_enable we clear the cpu_tsc_khz variable to zero and make sure
> it is set before running on a VCPU.
>
>   					  CPUFREQ_TRANSITION_NOTIFIER);
> +		for_each_online_cpu(cpu)
> +			per_cpu(cpu_tsc_khz, cpu) = cpufreq_get(cpu);
> +	} else {
> +		for_each_possible_cpu(cpu)
> +			per_cpu(cpu_tsc_khz, cpu) = tsc_khz;
> +	}
> +	for_each_possible_cpu(cpu) {
> +		printk(KERN_DEBUG "kvm: cpu %d = %ld khz\n",
> +			cpu, per_cpu(cpu_tsc_khz, cpu));
>   	}
>   }
>    

Leftover debug code?

-- 
error compiling committee.c: too many arguments to function

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