GNU bug report logs -
#6658
[PATCH] randread: don't require -lrt
Previous Next
Reported by: Paul Eggert <eggert <at> CS.UCLA.EDU>
Date: Fri, 16 Jul 2010 21:18:01 UTC
Severity: normal
Tags: patch
Done: Pádraig Brady <P <at> draigBrady.com>
Bug is archived. No further changes may be made.
Full log
View this message in rfc822 format
[Message part 1 (text/plain, inline)]
Your bug report
#6658: [PATCH] randread: don't require -lrt
which was filed against the coreutils package, has been closed.
The explanation is attached below, along with your original report.
If you require more details, please reply to 6658 <at> debbugs.gnu.org.
--
6658: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6658
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems
[Message part 2 (message/rfc822, inline)]
On 23/07/10 23:20, Paul Eggert wrote:
>>> 3. We could get about 2X CPU performance on 64-bit machines by using
>>> ISAAC64 instead of ISAAC.
>>>
>> These are all welcome changes, and the patch for (1) looks fine.
>
> OK, here's the change for (3), which I just pushed. I verified that
> it improved performance of random-number generation by 2x on my
> 64-bit host (RHEL 5 host with a Xeon E5620; the benchmark performance
> improvement was actually a tiny bit better than 2x speedup). On this
> platform isaac_refill now generates pseudorandom data at around 2.5 GB/s,
> which is quite a bit faster than /dev/urandom's 7.5 MB/s
> (as measured with dd).
Very nice.
> On 32-bit hosts the code behaves as before, though I expect it runs a
> bit faster than before (I haven't checked this).
Same performance on 32 bit here:
$ git pull origin
$ gcc -march=pentium-m -O2 -I lib gl/tests/test-rand-isaac.c lib/libcoreutils.a
$ time ./a.out 10000000
real 0m13.093s
$ (cd lib && make)
CC randread.o
CC rand-isaac.o
AR libcoreutils.a
$gcc -march=pentium-m -O2 -I lib gl/tests/test-rand-isaac.c lib/libcoreutils.a
$ time ./a.out 10000000
real 0m13.115s
Note I needed to comment out the ASSERT check
when linking with the old rand-isaac.
Is that a bug in the old implementation or just a change?
>
> Perhaps this stuff should be moved to gnulib? I can't recall if there
> was any good reason to leave it in coreutils.
>
Inertia more than anything I think.
> +++ b/gl/tests/test-rand-isaac.c
> +
> +/* FIXME: once/if in gnulib, use #include "macros.h" in place of this */
> +#define ASSERT(expr) \
Hmm, I just used macros.h in test-mbsalign.c which seems ok
I'm marking this rand update series as done.
cheers,
Pádraig.
[Message part 3 (message/rfc822, inline)]
In looking at the random part of coreutils some more, I see some
issues.
1. Apps that use random numbers typically must link to -lrt,
for a very small benefit (nanosecond resolution rather than
microsecond resolution time stamp for random seed). Often
this "benefit" is illusory as the time stamps really are not
nanosecond resolution.
2. If /dev/urandom is available, it should be used to seed
the ISAAC generator. This will cost more than invoking
gettimeofday() but it's far more random.
3. We could get about 2X CPU performance on 64-bit machines by using
ISAAC64 instead of ISAAC.
The patch below implements (1); I haven't installed it. I'd like to
do (2) and (3) too, but thought I'd ask for feedback first.
From aa279ddf6d766ca8f280295632d14cfbf4926c5b Mon Sep 17 00:00:00 2001
From: Paul R. Eggert <eggert <at> cs.ucla.edu>
Date: Fri, 16 Jul 2010 14:02:08 -0700
Subject: [PATCH] randread: don't require -lrt
Programs like 'sort' were linking to -lrt in order to get
clock_gettime, but this was misguided: it wasted considerable
resources while gaining at most 10 bits of entropy. Almost nobody
needs the entropy, and there are better ways to get much better
entropy for people who do need it.
* gl/lib/rand-isaac.c (isaac_seed): Include <sys/time.h> not
"gethrxtime.h".
(isaac_seed): Use gettimeofday rather than gethrxtime.
* gl/modules/randread (Depends-on): Depend on gettimeofday
and not gethrxtime.
* src/Makefile.am (mktemp_LDADD, shred_LDADD, shuf_LDADD, sort_LDADD):
(tac_LDADD): Omit $(LIB_GETHRXTIME); no longer needed.
---
gl/lib/rand-isaac.c | 6 +++---
gl/modules/randread | 2 +-
src/Makefile.am | 7 +------
3 files changed, 5 insertions(+), 10 deletions(-)
diff --git a/gl/lib/rand-isaac.c b/gl/lib/rand-isaac.c
index 52d53a3..377caa6 100644
--- a/gl/lib/rand-isaac.c
+++ b/gl/lib/rand-isaac.c
@@ -35,10 +35,9 @@
#include "rand-isaac.h"
#include <string.h>
+#include <sys/time.h>
#include <unistd.h>
-#include "gethrxtime.h"
-
/* This index operation is more efficient on many processors */
#define ind(mm, x) \
@@ -292,7 +291,8 @@ isaac_seed (struct isaac_state *s)
{ gid_t t = getgid (); ISAAC_SEED (s, t); }
{
- xtime_t t = gethrxtime ();
+ struct timeval t;
+ gettimeofday (&t, NULL);
ISAAC_SEED (s, t);
}
diff --git a/gl/modules/randread b/gl/modules/randread
index 9870cc8..efc7958 100644
--- a/gl/modules/randread
+++ b/gl/modules/randread
@@ -11,7 +11,7 @@ Depends-on:
error
exitfail
fopen-safer
-gethrxtime
+gettimeofday
quotearg
stdbool
stdint
diff --git a/src/Makefile.am b/src/Makefile.am
index d87fbb5..1a19fa6 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -328,13 +328,8 @@ ls_LDADD += $(LIB_CLOCK_GETTIME)
pr_LDADD += $(LIB_CLOCK_GETTIME)
touch_LDADD += $(LIB_CLOCK_GETTIME)
-# for gethrxtime, randint, randread, gen_tempname, mkstemp
+# for gethrxtime
dd_LDADD += $(LIB_GETHRXTIME)
-mktemp_LDADD += $(LIB_GETHRXTIME)
-shred_LDADD += $(LIB_GETHRXTIME)
-shuf_LDADD += $(LIB_GETHRXTIME)
-sort_LDADD += $(LIB_GETHRXTIME)
-tac_LDADD += $(LIB_GETHRXTIME)
# for cap_get_file
ls_LDADD += $(LIB_CAP)
--
1.7.1
This bug report was last modified 15 years and 2 days ago.
Previous Next
GNU bug tracking system
Copyright (C) 1999 Darren O. Benham,
1997,2003 nCipher Corporation Ltd,
1994-97 Ian Jackson.