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[76.191.17.161]) by smtp.googlemail.com with ESMTPSA id y74-20020a6bc84d000000b00645dfdd8a4csm8622442iof.38.2022.03.28.15.09.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Mar 2022 15:09:46 -0700 (PDT) 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 Message-Id: <20220328220936.2724834-2-goldstein.w.n@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220328220936.2724834-1-goldstein.w.n@gmail.com> References: <20220328220936.2724834-1-goldstein.w.n@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-12.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Noah Goldstein via Libc-alpha From: Noah Goldstein Reply-To: Noah Goldstein Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" `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 + . */ + +#include + +/* 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 (); +}