From: Paul Eggert <eggert@cs.ucla.edu>
To: Nix <nix@esperi.org.uk>
Cc: Achim Gratz <Stromeko@nexgo.de>, emacs-devel@gnu.org
Subject: Re: random doesn't feel very random
Date: Tue, 04 Sep 2012 13:07:41 -0700 [thread overview]
Message-ID: <50465F8D.2030706@cs.ucla.edu> (raw)
In-Reply-To: <87392xmw9a.fsf@spindle.srvr.nix>
On 09/04/2012 12:19 PM, Nix wrote:
> I'd recommend using /dev/urandom unconditionally,
> certainly for rare seeding operations
Yes, gnulib will have a module to do that, and that's
good enough for rare operations, but it's not enough
in general. Applications like 'shred' need lots of random
data and /dev/urandom is too slow for that. For example,
on my platform (AMD Phenom II X4 910e, x86-64, Fedora 17,
coreutils 8.19):
$ time dd if=/dev/urandom of=/dev/null ibs=12k obs=12k count=100000
100000+0 records in
100000+0 records out
1228800000 bytes (1.2 GB) copied, 92.9543 s, 13.2 MB/s
real 1m32.957s
user 0m0.100s
sys 1m32.563s
$ time shred --size=1200000k --iterations=1 /dev/null
real 0m0.670s
user 0m0.491s
sys 0m0.072s
Both applications wrote the same amount of random data to
/dev/null, using the same 12k blocksize.
Originally, 'shred' used /dev/urandom, but users
(rightly) complained that it was a pig, so we went with
something faster -- in this example, over 100x faster.
next prev parent reply other threads:[~2012-09-04 20:07 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-24 5:47 random doesn't feel very random Ivan Kanis
2012-08-24 6:22 ` Tassilo Horn
2012-08-24 17:19 ` random doesn't feel very random, random doesn't feel very random, " Ivan Kanis
2012-08-24 18:50 ` Stephen J. Turnbull
2012-08-25 7:46 ` Ivan Kanis
2012-08-24 6:30 ` Leo
2012-08-24 22:48 ` Richard Stallman
2012-08-24 22:57 ` Andreas Schwab
2012-08-25 20:55 ` Richard Stallman
2012-08-25 23:25 ` Leo
2012-08-26 13:12 ` Richard Stallman
2012-08-26 14:24 ` Achim Gratz
2012-08-26 23:22 ` Leo
2012-08-27 0:50 ` Stefan Monnier
2012-08-27 6:31 ` Simon Leinen
2012-08-27 3:41 ` Richard Stallman
2012-08-27 4:48 ` Stefan Monnier
2012-08-31 9:41 ` Eli Zaretskii
2012-08-31 15:06 ` Stefan Monnier
2012-08-31 15:23 ` chad
2012-08-31 17:50 ` Eli Zaretskii
2012-08-31 19:43 ` Stefan Monnier
2012-09-01 1:18 ` Paul Eggert
2012-09-01 7:19 ` Achim Gratz
2012-09-01 13:19 ` Paul Eggert
2012-09-04 19:19 ` Nix
2012-09-04 20:07 ` Paul Eggert [this message]
2012-09-04 20:11 ` Nix
2012-09-02 12:27 ` Jason Rumney
2012-09-02 13:08 ` Stefan Monnier
2012-09-01 7:22 ` Ivan Kanis
2012-09-01 11:13 ` joakim
2012-08-31 23:04 ` Leo
2012-08-27 5:17 ` Achim Gratz
2012-08-31 9:42 ` Eli Zaretskii
2012-08-31 15:07 ` Stefan Monnier
2012-08-31 17:50 ` Eli Zaretskii
2012-08-26 9:06 ` Ivan Kanis
2012-08-24 7:03 ` Stephen J. Turnbull
2012-08-24 9:10 ` Paul Eggert
2012-08-24 17:45 ` Stephen J. Turnbull
2012-08-24 12:45 ` OT: appropriateness of "random" for playlist generation (was: random doesn't feel very random) Jeremiah Dodds
2012-08-24 14:37 ` random doesn't feel very random Drew Adams
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