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Date:      Thu, 31 May 2012 16:28:20 -0400
From:      Jung-uk Kim <jkim@FreeBSD.org>
To:        Andriy Gapon <avg@freebsd.org>
Cc:        freebsd-stable@freebsd.org, Yamagi Burmeister <lists@yamagi.org>, seanbru@yahoo-inc.com
Subject:   Re: [stable 9] broken hwpstate calls
Message-ID:  <4FC7D464.20602@FreeBSD.org>
In-Reply-To: <4FC0A3A1.80200@FreeBSD.org>
References:  <1337319129.2915.4.camel@powernoodle-l7> <4FB6765A.2050307@FreeBSD.org> <1337710214.2916.8.camel@powernoodle-l7.corp.yahoo.com> <20120525163653.b61a08e2.lists@yamagi.org> <4FBFA9A9.7020806@FreeBSD.org> <4FBFBD39.7000105@FreeBSD.org> <4FBFDFFB.9020501@FreeBSD.org> <4FBFE624.1020208@FreeBSD.org> <20120526090233.f638c1d2.lists@yamagi.org> <4FC0A3A1.80200@FreeBSD.org>

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On 2012-05-26 05:34:25 -0400, Andriy Gapon wrote:
> on 26/05/2012 10:02 Yamagi Burmeister said the following:
>> On Fri, 25 May 2012 16:05:56 -0400 Jung-uk Kim <jkim@FreeBSD.org>
>> wrote:
>> 
>>>> if we decide so, then I think that we could still keep the
>>>> things "simple". As we currently use the "wholesale" approach
>>>> (all CPUs are set to the same P-state regardless of
>>>> topology), then we could first make a pass of writing the MSR
>>>> on all processors with a new P-state value and then make
>>>> another pass of checking via MSR C001_0063 that the P-state
>>>> is acquired.
>>> 
>>> No, I believe checking MSRC001_0071[18:16] is much simpler if
>>> it works. And it does not break current cpufreq(4) design
>>> principles.
>> 
>> Okay, thank's for your input. I'll come up with a patch. But it
>> won't happen until tuesday or wednesday next week.
>> 
> 
> I believe the approach that I suggested to be so trivial to
> implement (and also correct) that here is a patch:
...

It is simple but I don't like locking scheduler, binding CPU, and
writing the same MSR, multiple times for each core.  Besides, it
introduces more delay and you may be reading the correct status
because of that. :-P

If people really think checking MSRC001_0071[18:16] is unworthy for
Bulldozer, I prefer skipping status check but I disagree with this patch.

Thanks,

Jung-uk Kim
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