[PD] [bob~] denormals issue?

[Miller Puckette]

Yeah, I want to find out more about that :)

M

On Thu, Sep 22, 2016 at 12:01:31AM +0200, Christof Ressi wrote:
> I tried your patch with the [bob~] object shipped with the Windows binaries. I clearly get subnormals! It's actually no wonder because there isn't any protection against subnormals in the code (at least I couldn't spot it). 
> But the weird thing is: the [bob~] I compiled myself would also show subnormals in your patch but the CPU load is not affected...
> 
> > Gesendet: Mittwoch, 21. September 2016 um 23:47 Uhr
> > Von: katja <katjavetter at gmail.com>
> > An: "Christof Ressi" <christof.ressi at gmx.at>
> > Cc: "pd-list at lists.iem.at" <pd-list at lists.iem.at>
> > Betreff: Re: Re: Re: [PD] [bob~] denormals issue?
> >
> > Without -O flags you get debug-level and all function inlining is
> > disabled, depending on the code it can make a huge difference indeed.
> > But Pd is probably compiled with at least -O2. So the flags don't make
> > much difference. The compiler? Doesn't Miller compile with MinGW
> > nowadays, I don't know. MinGW brings its own standard C libs, which
> > may implement math functions differently than MS. But regarding
> > denormals I guess they both respect the IEEE 754 standard.
> > 
> > You can check if you really have subnormals using attached patch
> > denorm-test.pd you. The patch tests lop~, change it to bob~.
> > 
> > On Wed, Sep 21, 2016 at 11:18 PM, Christof Ressi <christof.ressi at gmx.at> wrote:
> > > the SSE optimizations don't seem to matter at all. skipping -ffast-math gives a slight overall CPU rise, while skipping -O3 gives me huge CPU rise (20 bob~ filters are already to much for one core). Even when skipping all of those flags, the denormals issue is still not present.
> > >
> > > Maybe it has something to do with the compiler?
> > >
> > >> Gesendet: Mittwoch, 21. September 2016 um 22:47 Uhr
> > >> Von: katja <katjavetter at gmail.com>
> > >> An: "Christof Ressi" <christof.ressi at gmx.at>, "pd-list at lists.iem.at" <pd-list at lists.iem.at>
> > >> Betreff: Re: Re: [PD] [bob~] denormals issue?
> > >>
> > >> I'm curious to know if the flags do flush denormals on your processor.
> > >> Forgot to mention that '-O3 -ffast-math' are also set,
> > >> platform-independent. So if you have a chance to try which flag does
> > >> something... It's just curiosity.
> > >>
> > >> On Wed, Sep 21, 2016 at 10:34 PM, Christof Ressi <christof.ressi at gmx.at> wrote:
> > >> > Hi Katja,
> > >> >
> > >> >> Even if your test reveals a beneficial effect from compiler flags,
> > >> >> it is better when denormals are detected and flushed in the C code.
> > >> >
> > >> > definitely! Maybe using the PD_BIGORSMALL macro on each filter state at the end of the DSP routine does the trick, just like in all the other recursive filters in Pd.
> > >> >
> > >> >
> > >> >
> > >> >> Von: katja <katjavetter at gmail.com>
> > >> >> An: "Christof Ressi" <christof.ressi at gmx.at>
> > >> >> Cc: pd-list <pd-list at iem.at>, "Miller Puckette" <msp at ucsd.edu>
> > >> >> Betreff: Re: [PD] [bob~] denormals issue?
> > >> >>
> > >> >> Hi Christof,
> > >> >>
> > >> >> Makefile.pdlibbuilder passes flags '-march=pentium4 -msse -msse2
> > >> >> -mfpmath=sse' for optimization to the compiler on Windows. You could
> > >> >> try compiling without (some of) these flags to see if they are
> > >> >> responsible for the different behavior. Makefile-defined optimization
> > >> >> flags can be overriden with argument CFLAGS given on command line.
> > >> >>
> > >> >> The effect of optimization flags on denormals varies per processor
> > >> >> type, unfortunately. When we had denormals on Raspberry Pi ARMv6 they
> > >> >> wouldn't go away no matter what flags, is what I remember. Even if
> > >> >> your test reveals a beneficial effect from compiler flags, it is
> > >> >> better when denormals are detected and flushed in the C code. Anyway,
> > >> >> it is still interesting to know what makes the difference.
> > >> >>
> > >> >> Katja
> > >> >>
> > >> >> On Wed, Sep 21, 2016 at 12:32 AM, Christof Ressi <christof.ressi at gmx.at> wrote:
> > >> >> > Hmmm... I compiled [bob~] myself with MinGW and pd-lib-builder and I noticed two things:
> > >> >> > 1) the CPU rise is gone
> > >> >> > 2) it needs only half the CPU. I put 20 [bob~] objects in a switched subpatch and measured the CPU load. The DLL which comes with the Windows binaries needs 15%, while my own DLL needs only 7%! That's quite a deal...
> > >> >> >
> > >> >> > Christof
> > >> >> >
> > >> >> > PS: I attached the DLL in case you wanna try it yourself.
> > >> >> >
> > >> >> >
> > >> >> >> Gesendet: Samstag, 17. September 2016 um 22:58 Uhr
> > >> >> >> Von: "Christof Ressi" <christof.ressi at gmx.at>
> > >> >> >> An: pd-list at iem.at, "Miller Puckette" <msp at ucsd.edu>
> > >> >> >> Betreff: [PD] [bob~] denormals issue?
> > >> >> >>
> > >> >> >> Hi Miller,
> > >> >> >>
> > >> >> >> feeding audio into [bob~] and then going to zero will increase the CPU load by ca. 6%. Clearing the filter or adding a tiny amount of noise brings the CPU load back to its usual level immediately, so I guess it's a problem with denormals.
> > >> >> >> My Pd load meter won't really show the increase, but it's clearly visibly on Process Explorer.
> > >> >> >>
> > >> >> >> See my attached patch. Tried with Pd 0.47.1, Lenovo Thinkpad L440, Windows 7.
> > >> >> >>
> > >> >> >> Christof_______________________________________________
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> > >> >> >>
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> > >> >>
> > >>
> > 
> 
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