[PD] Raspberry Pi does denormals

[katja]

'Undenormalized' Pd build for Raspberry Pi is temporarily parked here
for testing purposes (will be removed when Miller's release is fixed
in this sense):

www.katjaas.nl/temp/pd-0.44-0-normalized.tar.gz

This is a locally installed Pd, like Miller's distribution. You can
start it from command line with the full path to
pd-0.44-0-normalized/bin/pd. It's not a .deb, so it can't be installed
under supervision of package manager.

Katja


On Wed, Jan 23, 2013 at 9:15 PM, Julian Brooks <jbeezez at gmail.com> wrote:
> Hey Katja,
>
> Would you mind sharing the 'normalised' Pd-0.44.0 for RPi please.
>
> Cheers,
>
> Julian
>
>
>
> On 23 January 2013 18:23, katja <katjavetter at gmail.com> wrote:
>>
>> Now I recompiled the Pd-0.44.0 release on Raspberry Pi (took me a few
>> hours, not only because Pi is so slow) with PD_BIGORSMALL enabled for
>> arm in m_pd.h. Using bigorsmalltest.pd from my previous mail I
>> verified that the macro is implemented indeed.
>>
>> Martin Brinkmann's patch chaosmonster1
>> (http://www.martin-brinkmann.de) gives a beautiful illustration of the
>> improvement. This patch is full of filters and delay lines. At it's
>> initial settings, there is no subnormals problem. But if you set the
>> bottom slider to the right, it gets silent. With Pd-0.44-0 release,
>> CPU load explodes. With the 'normalized' Pd, nothing special happens.
>>
>> And indeed, the PD_BIGORSMALL conditional checks come for free: with
>> initial settings of the chaosmonster1, performance is equivalent in
>> both Pd's. Cool! Hopefully this is similar on armv7.
>>
>> Katja
>>
>>
>>
>> On Wed, Jan 23, 2013 at 5:01 PM, Hans-Christoph Steiner <hans at at.or.at>
>> wrote:
>> >
>> > hey Katya,
>> >
>> > This also sounds like good evidence for your idea of writing C code that
>> > modern compilers optimize well.  Using unions for aliasing allows the
>> > compiler
>> > to do all the new tricks, then writing loops that auto-vectorize gives
>> > us the
>> > real benefits.  Also, I think we can see some gains by using memcpy()
>> > since on
>> > modern libc version, those are highly optimized for the given CPU,
>> > dynamically
>> > choosing the routines based on what instructions are available. memcpy
>> > will
>> > use things like SSSE2 if its available.
>> >
>> > .hc
>> >
>> > On 01/23/2013 07:47 AM, katja wrote:
>> >> Finally some good news on this topic. Earlier I stated that 'big or
>> >> small tests' are expensive for the Pi, but that is not by definition
>> >> the case. There must have been other conditions blurring my
>> >> impression. I've now done a systematic test where other influences are
>> >> ruled out. A test class [lopass~] with exactly the same routine as
>> >> [lop~] was made, but compiled with PD_BIGORSMALL() macro enabled. It
>> >> was verified that [lopass~] is not affected by denormals. Performance
>> >> comparison of [lop~] and [lopass~] shows that both objects cause
>> >> equivalent CPU load. Meaning, Raspberry Pi gives the 'big or small
>> >> checks' for free! At least in the case of this simple filter. Please
>> >> try attached bigorsmalltest.zip on the Pi to see if I'm not dreaming.
>> >>
>> >> While I was at the topic anyway, I also tried a big or small test with
>> >> union instead of direct type aliasing. It has the advantage that the
>> >> compiler can apply strict aliasing rules. This test with unions did
>> >> not cause extra CPU load either on the Pi. If you want to verify this
>> >> result, enable the call to bigorsmall() instead of PD_BIGORSMALL in
>> >> lopass~.c and recompile.
>> >>
>> >> The fact that these tests do not cause extra CPU load, indicate that
>> >> they are done in parallel with other instructions. Float and int
>> >> registers are apparently strictly separated on armv6, there's no such
>> >> thing like Intel's xmm registers or armv7's NEON. As it happens, the
>> >> big or small tests are done on ints, aliases of the floats that must
>> >> be tested. Initially I assumed that the transport of floats from vfp
>> >> to the arm integer processor would be expensive, but if the
>> >> instructions are done simultaneously it may be an advantage instead.
>> >> Another thing is that ARM implements branch predication instead of
>> >> branch prediction. Those terms look almost the same but the routines
>> >> are very different. Predication is when instructions for both branches
>> >> are executed, and the wrong result is simply discarded later.
>> >>
>> >> Conclusions from the limited test with [lop~] and [lopass~] do not
>> >> mean that all sorts of conditional checks are cheap on the Pi, or on
>> >> ARM in general. If PD_BIGORSMALL is enabled for RPi using compile-time
>> >> definition __arm__, it will also hold for armv7, but it may have very
>> >> different result there. At the moment I have no access yet to an armv7
>> >> device. Maybe someone can recompile test class [lopass~] and do the
>> >> tests on Beagleboard or Cubieboard? Otherwise I may be able to do it
>> >> on my friend's PengPod when that has arrived.
>> >>
>> >> Katja
>> >>
>> >>
>> >> On Tue, Jan 22, 2013 at 8:54 PM, Miller Puckette <msp at ucsd.edu> wrote:
>> >>> thanks - I'd better try this and find out what's going on :)
>> >>>
>> >>> M
>> >>>
>> >>> On Mon, Jan 21, 2013 at 11:54:29AM +0100, katja wrote:
>> >>>> Tried the 0.44.0 build from your website. It has the same issue with
>> >>>> subnormal values. My test patch is with [lop~]. If inf or nan is fed
>> >>>> into [lop~], these 'values' keep circulating in the object, it can no
>> >>>> longer process normal signal values.
>> >>>>
>> >>>> I also tried my reverb stuff with specific compiler options for Pi's
>> >>>> processor:
>> >>>>
>> >>>> -march=armv6zk
>> >>>> -mcpu=arm1176jzf-s
>> >>>> -mtune=arm1176jzf-s
>> >>>>
>> >>>> With these options, gcc should be able to decide that RunFast mode is
>> >>>> permitted. But even in combination with -ffast-math (which in turn
>> >>>> sets -funsafe-math-optimizations and -fno-trapping-math amongst
>> >>>> others), denormals are still there. I'm literally out of options for
>> >>>> the moment. Sorry for not having better news.
>> >>>>
>> >>>> Katja
>> >>>>
>> >>>>
>>
>> _______________________________________________
>> Pd-list at iem.at mailing list
>> UNSUBSCRIBE and account-management ->
>> http://lists.puredata.info/listinfo/pd-list
>
>