From: Noah Goldstein <goldstein.w.n@gmail.com>
To: libc-alpha@sourceware.org
Subject: [PATCH v1 2/2] x86: Use rdtsc for generating entropy for random_bits
Date: Mon, 28 Mar 2022 17:09:36 -0500 [thread overview]
Message-ID: <20220328220936.2724834-2-goldstein.w.n@gmail.com> (raw)
In-Reply-To: <20220328220936.2724834-1-goldstein.w.n@gmail.com>
`rdtsc` generates a comparable amount of entropy and is faster than
`clock_gettime`.
Entropy:
random_bits w/ rdtsc:
Entropy = 7.805972 bits per byte.
random_bits w/ clock_gettime:
Entropy = 7.806116 bits per byte.
Measured entropy of `random_bits` using `rdtsc` vs `clock_gettime`
using ent: https://www.fourmilab.ch/random/
Performance:
random_bits w/: rdtsc, clock_gettime
throughput: 16.35, 38.36
latency: 23.68, 54.15
Time as cycles (measured with `rdtsc`) / Trials. benchmarks done on
Tigerlake.
---
sysdeps/x86_64/random-bits-entropy.h | 36 ++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
create mode 100644 sysdeps/x86_64/random-bits-entropy.h
diff --git a/sysdeps/x86_64/random-bits-entropy.h b/sysdeps/x86_64/random-bits-entropy.h
new file mode 100644
index 0000000000..1e96659aa3
--- /dev/null
+++ b/sysdeps/x86_64/random-bits-entropy.h
@@ -0,0 +1,36 @@
+/* Function for generating entropy quick on x86 with rdtsc.
+ Copyright (C) 2022 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <stdint.h>
+
+/* rdtsc is faster than generic (clock_gettime) and has roughly the same
+ entropy. Result of filling a file using random_bits with rdtsc vs
+ clock_gettime as an entropy function:
+
+ $> ent gettime-random.txt
+ Entropy = 7.806116 bits per byte.
+
+ $> ent rdtsc-random.txt
+ Entropy = 7.805972 bits per byte.
+ */
+
+static inline uint32_t
+random_bits_entropy (void)
+{
+ return __builtin_ia32_rdtsc ();
+}
--
2.25.1
next prev parent reply other threads:[~2022-03-28 22:09 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-28 22:09 [PATCH v1 1/2] random-bits: Factor out entropy generating function Noah Goldstein
2022-03-28 22:09 ` Noah Goldstein [this message]
2022-03-29 19:51 ` Adhemerval Zanella
2022-03-29 19:56 ` Noah Goldstein
2022-03-29 20:04 ` Noah Goldstein
2022-03-29 20:14 ` H.J. Lu
2022-03-29 20:44 ` Adhemerval Zanella
2022-03-29 20:52 ` Noah Goldstein
2022-03-29 20:37 ` Adhemerval Zanella
2022-03-29 20:44 ` Noah Goldstein
2022-03-30 15:37 ` Adhemerval Zanella
2022-03-30 16:30 ` Noah Goldstein
2022-03-30 19:38 ` Cristian Rodríguez
2022-03-31 4:45 ` Jason A. Donenfeld
2022-03-31 10:08 ` Cristian Rodríguez
2022-03-31 11:17 ` Adhemerval Zanella
2022-03-31 11:25 ` Cristian Rodríguez
2022-03-31 11:48 ` Adhemerval Zanella
2022-03-31 12:14 ` Cristian Rodríguez
2022-03-31 13:12 ` Yann Droneaud
2022-03-31 15:31 ` Jason A. Donenfeld
2022-03-31 18:16 ` Noah Goldstein
2022-03-31 21:57 ` Cristian Rodríguez
2022-03-31 22:33 ` Noah Goldstein
2022-03-31 22:51 ` Jason A. Donenfeld
2022-03-31 23:05 ` Noah Goldstein
2022-03-31 23:25 ` Jason A. Donenfeld
2022-04-01 18:01 ` Cristian Rodríguez
2022-04-04 17:42 ` Adhemerval Zanella
2022-04-04 18:23 ` Noah Goldstein
2022-04-04 18:38 ` Adhemerval Zanella
2022-04-04 18:52 ` Noah Goldstein
2022-04-04 19:20 ` Adhemerval Zanella
2022-04-04 19:48 ` Noah Goldstein
2022-04-04 19:57 ` Adhemerval Zanella
2022-04-04 14:51 ` Florian Weimer
2022-04-04 14:54 ` Jason A. Donenfeld
2022-04-04 15:00 ` Florian Weimer
2022-04-04 16:51 ` Noah Goldstein
2022-04-04 17:22 ` Adhemerval Zanella
2022-04-04 18:32 ` Jason A. Donenfeld
2022-04-04 19:16 ` Noah Goldstein
2022-04-05 0:10 ` Cristian Rodríguez
2022-04-05 0:18 ` Jason A. Donenfeld
2022-04-05 13:45 ` Cristian Rodríguez
2022-04-05 9:22 ` Florian Weimer
2022-04-04 18:28 ` Jason A. Donenfeld
2022-04-05 9:20 ` Florian Weimer
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