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Re: CPU and GC cost of bignums
From: |
Ludovic Courtès |
Subject: |
Re: CPU and GC cost of bignums |
Date: |
Wed, 05 Feb 2020 17:29:30 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) |
Hey ho!
Ludovic Courtès <address@hidden> skribis:
> … but has the disadvantage that it doesn’t work: ‘numbers.test’ fails
> badly on bignums.
I think with the excitement I no longer knew what I was saying. So,
here’s a revised patch that actually preserves memory management (as in:
‘mpz_t’ are eventually freed), while getting rid of finalizers. Result:
--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use(system base optimize)
scheme@(guile-user)> ,use(statprof)
scheme@(guile-user)> (gcprof (lambda () (compile-file "gnu/services/mail.scm"
#:opts (optimizations-for-level 1))))
% cumulative self
time seconds seconds procedure
25.00 3.25 3.25 anon #x66e8e0
9.38 2.44 1.22 language/cps/intset.scm:551:2:union
6.25 0.81 0.81 ice-9/boot-9.scm:2201:0:%load-announce
6.25 0.81 0.81 anon #x66e468
3.13 139.83 0.41 ice-9/threads.scm:388:4
3.13 73.57 0.41 language/tree-il/peval.scm:710:2:loop
3.13 4.47 0.41 system/vm/assembler.scm:1201:0:intern-constant
3.13 1.63 0.41 ice-9/psyntax.scm:2964:6:match*
3.13 1.22 0.41 language/cps/intset.scm:270:2:adjoin
3.13 0.81 0.41 language/cps/intmap.scm:184:0:intmap-add!
3.13 0.41 0.41 language/cps/slot-allocation.scm:843:19
[...]
Sample count: 32
Total time: 13.007326523 seconds (4.420918875 seconds in GC)
--8<---------------cut here---------------end--------------->8---
I’d like to go ahead with this patch if there are no objections!
Ludo’.
diff --git a/libguile/numbers.c b/libguile/numbers.c
index d1b463358..8606780a8 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -1,4 +1,4 @@
-/* Copyright 1995-2016,2018-2019
+/* Copyright 1995-2016,2018-2020
Free Software Foundation, Inc.
Portions Copyright 1990-1993 by AT&T Bell Laboratories and Bellcore.
@@ -218,16 +218,6 @@ static mpz_t z_negative_one;
-/* Clear the `mpz_t' embedded in bignum PTR. */
-static void
-finalize_bignum (void *ptr, void *data)
-{
- SCM bignum;
-
- bignum = SCM_PACK_POINTER (ptr);
- mpz_clear (SCM_I_BIG_MPZ (bignum));
-}
-
/* The next three functions (custom_libgmp_*) are passed to
mp_set_memory_functions (in GMP) so that memory used by the digits
themselves is known to the garbage collector. This is needed so
@@ -237,19 +227,20 @@ finalize_bignum (void *ptr, void *data)
static void *
custom_gmp_malloc (size_t alloc_size)
{
- return scm_malloc (alloc_size);
+ return scm_gc_malloc (alloc_size, "GMP");
}
static void *
custom_gmp_realloc (void *old_ptr, size_t old_size, size_t new_size)
{
- return scm_realloc (old_ptr, new_size);
+ return scm_gc_realloc (old_ptr, old_size, new_size, "GMP");
}
static void
custom_gmp_free (void *ptr, size_t size)
{
- free (ptr);
+ /* Do nothing: all memory allocated by GMP is under GC control and
+ will be freed when needed. */
}
@@ -260,12 +251,10 @@ make_bignum (void)
scm_t_bits *p;
/* Allocate one word for the type tag and enough room for an `mpz_t'. */
- p = scm_gc_malloc_pointerless (sizeof (scm_t_bits) + sizeof (mpz_t),
- "bignum");
+ p = scm_gc_malloc (sizeof (scm_t_bits) + sizeof (mpz_t),
+ "bignum");
p[0] = scm_tc16_big;
- scm_i_set_finalizer (p, finalize_bignum, NULL);
-
return SCM_PACK (p);
}