[PD] [bob~] denormals issue?

[katja]

On Linux i386 bob~ produces subnormals as well and very high cpu load.
It is not the slowly decaying signal that other filters tend to give,
but a quick decay to a fixed small number.

It's weird indeed when subnormals cause different CPU load depending
on how they are compiled. Since MinGW is a gcc port I would think it
uses the same math implementation which produces such high CPU load
for bob~ subnormals on my system.

On Thu, Sep 22, 2016 at 12:01 AM, Christof Ressi <christof.ressi at gmx.at> 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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