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Date: Thu, 29 May 2014 00:53:38 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Doug Smythies <dsmythies@telus.net>
Cc: "'Johan Hovold'" <jhovold@gmail.com>,
        "'Dirk Brandewie'" <dirk.brandewie@gmail.com>,
        "'Viresh Kumar'" <viresh.kumar@linaro.org>, dirk.j.brandewie@intel.com,
        "'Rafael J. Wysocki'" <rafael.j.wysocki@intel.com>,
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        "'Greg Kroah-Hartman'" <gregkh@linuxfoundation.org>,
        "'Stratos Karafotis'" <stratosk@semaphore.gr>
Subject: Re: Performance regression in v3.14
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> That is not true. Yes, and due to the setpoint being less than
> 100, which is needed or the driver won't work at all, there is
> a tendency to drive the target pstate upwards.
> However that is tempered by both the PID proportional gain,
> and ultimately integer math. More importantly, the CPU
> itself tells the driver when it is operating below the target
> pstate and driver responds.
> 
> Additionally, the tendency to drive up the target pstate
> too much is exasperated by some extra rounding up at a
> couple of spots. Dirk has a pending fix.
> 
> > And a few iterations
> > later, we will reach max (possible) frequency,
> > then we are effectively performance governor
> > (highest frequency all the time).
> 
> Please do not confuse highest target pstate with
> highest frequency. They are not the same. The processor
> itself can back off.
> 
Hi Doug,

All you said is about the hardware will not give whatever software wants
(e.g., requested freq too high). Agreed.

But does it matter to this discussion?

Yuyang