[PD] Findings regarding performance

Roman Haefeli reduzent at gmail.com
Thu Dec 1 15:24:36 CET 2011

Hi all

Lately I was asking myself if some of own patching practices regarding
performance optimization were justified or based on some wrong beliefs.

I often use [*~ ] as on/off signal gates and now started be concerned
about using an object that performs a relatively complex task
(multiplication of two floating point numbers) for such a simple task. I
imagined that an object that either outputs a copy of the input or
outputs zeros would be a less expensive on/off signal gate than [*~]. I
created an abstraction containing this:

[inlet~]     [inlet]
|            |
|            [switch~ ]

Let's call this abstraction [gate~ ]. It turned out to work as supposed.
But is [gate~] really cheaper than [*~ ]? I made a test by connecting
lots of [gate~]s to a chain and measure the CPU usage. For simplicity
reason, let's just use an invented arbitrary unit for expressing the CPU
time (ct) consumed by an object. It turned out that [gate~] uses 0.52ct
when it is on and 0.4ct when it is off. But how much does [*~ ] use? No
matter whether turned on or off, [*~ ] uses a stable 0.39ct.

The relatively complex multiplication is _not_ more expensive than the
on/off implementation with [switch~ ]. Even when turned off, the
[switch~] approach is still more expensive.

But the really interesting finding comes now. [*~ 0] has only 0.2ct!
Almost the the ct value of a plain [*~ ] halved! It also doesn't matter
what value the argument has. The plain fact of specifying an argument
makes [*~ ] a lot cheaper. I also tested [/~ ], [+~ ] and [-~ ] and the
same applies for those. They all have 0.39ct without argument and only
0.2ct with an argument specified. Depending on the kind of patch, this
allows for quite a significant performance improvement.

I also measured the ct of a [*~ ] when a signal wire is connected to the
right inlet. It costs exactly as much (0.39ct) as when sending messages
to the right inlet of a [*~ ] without argument. 

My interpretation is that [*~ 0] and [*~ ] are two different objects.
The latter always performs a calculation with two signals and implicitly
converts a message on the right inlet to a signal, where the former
really only deals with messages on the right inlet (and thus is

On a completely different note, I wanted to know if it costs anything to
have signals entering and leaving subpatches and abstractions a lot,
respectively if [inlet~] and [outlet~] add some overhead in CPU time. I
chained tens of thousands subpatches together and it seems that does not
consume any additional CPU time at all. The values for [inlet~ ] and
[outlet~] are much below 0.01ct. I haven't tested the cost, when more
than one signal wire are going to an [inlet~], though. 


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