[XviD-devel] XViD Profiling Measured time != Overall time

Dark Sylinc dark_sylinc at yahoo.com.ar
Wed Dec 17 15:03:02 CET 2008

> Overall encoding time: 140.000000 ms, we measured 40.000000
> ms (28.571429
> percent) Or
> Overall encoding time: 160.000000 ms, we measured
> 100.000000 ms (62.500000
> percent) and never ever is the measured time equal to the
> overall time.

I'm confused "how" you measured it your self.

> Overall encoding time: 140.000000 ms,
> Overall encoding time: 160.000000 ms
20 milliseconds difference between 2 tests seems reasonable.
(a 14% increase)

>we measured 40.000000 ms
>we measured 100.000000 ms
a 250% increase in time taken seems huuughe.
So... how are you measuring it exactly?
Because your readings don't seem as stable as XviD's

Last minute revision:
I've checked CVS read_counter() and get_freq() before sending the mail:

1) We're using the rdtsc for god sake!! AFAIK rdtsc gets REALLY unstable (unnacurate) when combined with multi-core

2) get_freq() is really unacurrate too! Again, thanks to multi-core (not just multi core, but any kind of multi threading, even another process may interrupt this) and Cool 'n Quiet feature, get_freq() may return much smaller values than it should, resulting in higher times.

So after seeing this, I strongly feel Anwar Sajid is right.

We should be using gettimeofday for UNIX variants, and QueryPerformanceCounter in Windows.

Dark Sylinc

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