Hey Katja, Would you mind sharing the 'normalised' Pd-0.44.0 for RPi please.
Cheers, Julian On 23 January 2013 18:23, katja <[email protected]> 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 <[email protected]> > 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 <[email protected]> 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 > >>>> > >>>> > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list >
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