[PATCH] Linear regression in UPower

[Leonardo Robol]

Hi folks!

I am writing to propose a patch for UPower. I have a broken battery (or
ACPI, or what it is, I really don't know) and it doesn't report
energy-rate. From the last version UPower is able to compute the
discharge (or charge) rate by sampling the energy over time, that is a
really nice feature for me!

The thing is that only two points are used to compute this rate, and so
the time estimate is quite going up and down. I thought it would be nice
to use a simple linear regression [1] to determine the rate, so I wrote
a patch to the test the idea, and it is working for me.

Do you think the patch could be included upstream? I think that many
broken-batteries people would be glad to have a consistent estimate of
the remaining lifetime.
I understand, though, that this change make the rate change slowly in
response to some events (like starting heavy computations or so...) but
I still think that taking the average on some more points is nicer.

I'm attaching the patch to this email.

P.S.: The memmove() call are not the best way to handle prepending new
entries in the array; if you think it's nicer I could write a simple
circular buffer to store energy_old values and timespecs.

Thanks again for your work :)

[1]: http://en.wikipedia.org/wiki/Linear_regression
-- 
Leonardo Robol <leo at robol.it>
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