Re: imdct36 CPU usage increase
Derk-Jan Hartman <[email protected]>
| Newsgroups | gmane.comp.audio.mad.devel |
|---|---|
| Message-ID | <[email protected]> |
On 15 feb 2004, at 02:56, Rob Leslie wrote: > On Feb 14, 2004, at 7:30 AM, Derk-Jan Hartman wrote: >> For some strange reason our latest version of VLC OSX more than >> doubles the CPU usage of mad_frame_decode, specifically the imdct36 >> routine it would seem. It is an OS X problem only and very annoying. >> Decoding mp3 now requires 28% CPU usage on my G4/400 (used to be >> 12%). >> >> libmad library version changes have been ruled out as the cause of >> this. Our mp3 decoder module didn't change either, but the demux >> module did change. We suspect it might be something like an alignment >> issue, but we can't seem to track it down.. >> >> Could you give some advice as to what might be the cause of this >> sudden increase in CPU usage, and how me may check some of our input >> for correctness? > > I don't think alignment should be an issue since nothing in imdct36() > depends on the alignment of the bitstream. > > The only possibility I can see affecting the performance of imdct36() > might be a possible change in compilation directives. The preprocessor > symbols FPM_*, OPT_SPEED, and OPT_ACCURACY can all drastically affect > performance, as can the selection of compiler optimization flags. You > might check to make sure these have not changed. i configured mad to be as fast as possible and still it's twice as intensive as in the older release. I'm working with profiling data here, so it's a bit hard to detect the problem. However... Though imdct36 is taking the most time by far, I noticed that the difference is within III_decode() III_decode takes almost the same CPU time in both versions. however then the differences start. III_imdct_l takes 2.7% in old version and 7.8% in the new version. That imdct36() is called more often because of this is logical of course. So the problem is probably somewhere within III_decode() and causing III_imdct_l to be called more often than before... Any new ideas after this information? DJ --- Universiteit Twente Derk-Jan Hartman (d.hartman at student.utwente dot nl) http://home.student.utwente.nl/d.hartman