linux-kernel - Re: [PATCH v4: kvm 1/4] Code motion. Separate timer intialization into an indepedent function.

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Message-ID: <4AC38467.2060406@redhat.com>
Date:	Wed, 30 Sep 2009 06:16:39 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Avi Kivity <avi@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v4: kvm 1/4] Code motion.  Separate timer intialization
 into an indepedent function.

On 09/30/2009 06:11 AM, Avi Kivity wrote:
> On 09/30/2009 06:06 PM, Zachary Amsden wrote:
>> On 09/30/2009 05:56 AM, Avi Kivity wrote:
>>> On 09/30/2009 05:51 PM, Zachary Amsden wrote:
>>>
>>> If the API allows us to query the tsc frequency, it would simply 
>>> return the same values in all cases, which we'd ignore.
>>
>> The API only allows querying the processor frequency.  In the 
>> constant_tsc case, the highest processor frequency is likely going to 
>> be the actual TSC frequency, but I don't think it's a guarantee; 
>> theoretically, it could be faster on normal hardware ... or slower on 
>> overclocked hardware with an externally clocked TSC.
>
> Well we could add a new API then (or a new tscfreq notifier).  Those 
> conditionals don't belong in client code.

It's possible... but it's also possible to run without cpufreq enabled, 
which won't work properly unless the cpufreq code is aware of the 
measured tsc_khz...  this could be a little ugly architecture wise given 
the big melting pot of generic code and vendor / arch specific code here.

Since we're already very hardware dependent and one of the few clients 
who care, it seems okay to leave it as is for now.

Zach
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