[Chicken-users] Need help to figure out where this strange performance impact is coming from

[Jörg F . Wittenberger]

Hi Chickeneers,

yesterday I found that simply having a (use mailbox) in some code had a
huge impact (more than a factor of 3) at the performance of the
resulting executable.  Without using the mailbox stuff at all.

Meanwhile I figured out that this has nothing at all to do with the
mailbox egg.  But _all_ with the use of srfi-1.

But how is this possible?

Attached some test code.  As I ran into it from mailbox I prepared a
stripped down version of it to play with.  Towards the end of the file
there is a (use srfi-1) which makes all the difference.

So far I found (compiling the code with -O5 but similar things happen
with less aggressive optimization):

a) Using chicken 4.9.1 there is absolutely no difference.  Using srfi-1
or not I get roughly 100 messages passed per ms on my machine.  (But I
have to include the forced gc; see comment in the code.)

b) A slightly different version which avoids allocations in the queue
runs without the forced gc and yields about 160 ms^-1 on chicken 4.9.1
Again no difference whether or not I (use srfi-1) anywhere.

Now the interesting bits:

c) On master (built almost two weeks ago) I get - when (use srfi-1) is
included - about 180 ms^-1.  Those ~5% faster sound about right to me.

d) Comment out the (use srfi-1) at line 163 and it goes down to about
_50_ per millisecond!

e) The same happens for the alternative, allocation free version (not
attached), which uses vectors instead of pairs.


Speculating: The code I wrote has nothing to do with the difference.

But I'm confused.  Neither scheduler.scm nor srfi-18 seem to have any
dependency on srfi-1.  Also srfi-1 seems not to overwrite any global
bindings.

Should we simply always (use srfi-1) if we also (use srfi-18).  Looks
like a workaround, but not like the right thing to do.

How could I boil this down to the real reason?

Best

/Jörg

simple3.scm
Description: Text Data