Re: So, what's the status on the recent patches here?

[Matthew Locke <matthew.a.locke@comcast.net>]

On Aug 29, 2006, at 9:52 PM, David Singleton wrote:

> On 8/29/06, Pavel Machek <pavel@ucw.cz> wrote:
>> Hi!
>>>>>         point, by name. There is a new
>>>> /sys/power/operating_points directory
>>>>>         that shows all the operating points the
>>>> system supports. An
>>>>>         exampled from my centrino laptop shows:
>>>>>
>>>>>         /sys/power/operating_points/high
>>>>>         /sys/power/operating_points/highest
>>>>>         /sys/power/operating_points/low
>>>>>         /sys/power/operating_points/lowest
>>>>>         /sys/power/operating_points/medium
>>>>>         /sys/power/operating_points/mem
>>>>>         /sys/power/operating_points/standby
>>>>
>>>> What makes you think that mixing operating and sleep
>>>> states is good
>>>> idea?
>>>
>>> They are all power states managed by the kernel and in
>>> the operating
>>> point concept they are all operating points the system
>>> supports.
>>
>> That does not make mixing them right.
>
> Both OpPoint and PowerOp are going to 'mix' frequency, voltage
> and sleep states into their operating point concepts.

PowerOP does not mix sleep states with operating points.  We are not 
pushing for integrating sleep states and operating points.  I haven't 
seen an implementation that makes sense yet.  I'm writing another email 
to address this in more detail.

>
> The point was not to make it look like I was mixing sleep states and
> CPU frequency states, but to present all the power states
> supported by the system in one place and with one interface.  It 
> simplifies
> not only kernel code, but power manager code as well.
>
>>
>>> The system can be set to any of the supported states by
>>> setting their name in the /sys/power/state file.  I find
>>> simplicity
>>> is usually a good thing.
>>
>> I believe the quote is 'make it as simple as possible but not
>> simpler'.
>>
>>>> And '600MHz' makes lot more sense than 'lowest' on
>>>> centrino.
>>>
>>> Perhaps, but the common name space makes it easy for the
>>> power manager
>>> daemon to perform the same functions without having to
>>> know that the lowest
>>> speed on my laptop is 600Mhz.
>>
>> And enumerate english strings in power daemon? Limiting the numver of
>> states?
>
> Hah,  I didn't think of it that way.   I was thinking in the same way
> "mem" and "disk" and "standy" are strings in the kernel.
>
>  The names themselves don't mean anything other than to imply an order 
> so the
> kernel and power manager can understand the same order.
>
> I have the oppointd daemon running on systems of different 
> architectures
> and different numbers of operating points.  Some have only two 
> operating
> points defined, some have three, some have five and one has six.
>
> The power manager functions the same on all of them because of the 
> ordering
> presented by the names.
>
> The oppointd daemon also understands that the operating points 
> associated
> with the names  may be sparsely populated.  The daemon can  still work
> correctly on a sparsely populated name space because of the ordering
> implied. It works unchanged
> on systems with only two states and on systems with six states.
>
>>
>>>>
>>>>>         /sys/power/operating_points/high/frequency
>>>>>         /sys/power/operating_points/high/voltage
>>>>>         /sys/power/operating_points/high/latency
>>>>
>>>> What is voltage for 'mem'?
>>>
>>> I don't know what the voltage or latency is for mem.
>>> Perhaps Intel could better
>>> say what the voltage is in the suspend state and what
>>> the latency was
>>> for transistion to that state.  I didn't have the data
>>> available when
>>> I wrote the code.
>>
>> And you will not have data available even if intel helps you. What is
>> _frequency_ for mem? These fields are meaningless for sleep states;
>> that should tell you that mixing sleep and operating states is bad
>> idea.
>
> Actually the SoC concerns that both OpPoint and PowerOp are trying
> to deal with have different power consumption levels associated with
> different sleep states.
>
> Different sleep states have different power consumption levels
> and different transition latencies.  The power manager needs to
> understand both the power consumption level with each
> sleep state and the transition latency so it can make decisions
> about when to transition into different sleep states.
>
> Typically sleep states with the lowest power consumption have
> the longest transition latencies.  The power manager must know
> the power consumption and transition latencies so it can decide when 
> best to
> switch to a sleep state that consumes a bit more power but has
> a much shorter latency to switch into and out of,  and
> when it's okay to switch to the lowest sleep state, but longest
> transition latency.
>

Latency is a good example of how mixing sleep states with operating 
points doesn't  quite work.  Latency for switching to a new operating 
point is very a much a function of the current operating point.   I 
think latency for sleep states is the same every time.  Also which 
direction are you capturing latency for, suspend or resume?  If your 
power manager is making decisions based on latency, I could imagine 
that it needs to know the latency for going into and out of that state.

>>
>> --
>> Thanks for all the (sleeping) penguins.
>>
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