[Ecls-list] Slow bignums

[Juan Jose Garcia-Ripoll]

On Sat, Jan 30, 2010 at 3:12 AM, Waldek Hebisch <hebisch at math.uni.wroc.pl>wrote:
>
> Yes, typically copy is cheap enough.  But in this case main operations
> are adding 1 and multiplication by fixnum.  Adding 1 costs basically
> the same as copy.  Multiplication by fixnum is slightly more expensive,
> but should be no more expensive than two copies.
>

Waldek, sorry if I sound rude, but really, you are talking out of
conjectures without paying attention to my previous emails. I told you the
results from profiling when using registers: 80% time on my Mac is spent in
the garbage collection routine (most of it in the conservative mark phase),
10% in allocation, 10% in the bignum library or less. Now without registers
those numbers only changed by 5% or so. I also offered you the numbers from
a 64-bits platform where the garbage collector is much better because
pointers are very much more spread and only a tiny fraction of the address
space is filled. There ECL can beat SBCL without problems, and I bet the
profiling numbers regarding garbage collection are still large.

You mean that ECL _always_ shrinks register if it gets large?  That
> looks like huge waste.  It looks like nice opportunity to use
> weak references: keep weak reference to register and let garbage
> collector to recycle it.  But before garbage collection register
> would still be available for reuse.


The Boehm-Weiser garbage collector can be triggered at any time. We do not
have control on that, specially on multithreaded systems. Thus to decide
whether we kill or not a bignum register is used is something out of our
control. But most important, if the garbage collector decides a register is
not reachable and garbage collects it, then we will have to allocate it
again, which is a cost one avoids by having the register in the first place.

In any case, I repeat that this is all talk of the past. Bignum registers
are now only restricted to FLOOR & co, bignum reading, and a few other
routines. And times have not changed that much due to this.

Juanjo

-- 
Instituto de Física Fundamental, CSIC
c/ Serrano, 113b, Madrid 28006 (Spain)
http://juanjose.garciaripoll.googlepages.com
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