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[76.191.17.161]) by smtp.googlemail.com with ESMTPSA id t18-20020a056e02011200b002cbe6ce18e5sm113120ilm.40.2022.04.13.21.12.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Apr 2022 21:12:41 -0700 (PDT) From: Noah Goldstein To: libc-alpha@sourceware.org Subject: [PATCH v1 5/6] nss: Optimize nss_hash in nss_hash.c Date: Wed, 13 Apr 2022 23:12:30 -0500 Message-Id: <20220414041231.926415-5-goldstein.w.n@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220414041231.926415-1-goldstein.w.n@gmail.com> References: <20220414041231.926415-1-goldstein.w.n@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-11.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, LIKELY_SPAM_BODY, 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-List-Received-Date: Thu, 14 Apr 2022 04:12:44 -0000 The prior unrolling didn't really do much as it left the dependency chain between iterations. Unrolled the loop for 4 so 4x multiplies could be pipelined in out-of-order machines. Results for __nss_hash Benchmarked on Tigerlake: 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz Time as Geometric Mean of N=25 runs Geometric of all benchmark New / Old: 0.845 type, length, New Time, Old Time, New Time / Old Time fixed, 0, 4.019, 3.729, 1.078 fixed, 1, 4.95, 5.707, 0.867 fixed, 2, 5.152, 5.657, 0.911 fixed, 3, 4.641, 5.721, 0.811 fixed, 4, 5.551, 5.81, 0.955 fixed, 5, 6.525, 6.552, 0.996 fixed, 6, 6.711, 6.561, 1.023 fixed, 7, 6.715, 6.767, 0.992 fixed, 8, 7.874, 7.915, 0.995 fixed, 9, 8.888, 9.767, 0.91 fixed, 10, 8.959, 9.762, 0.918 fixed, 11, 9.188, 9.987, 0.92 fixed, 12, 9.708, 10.618, 0.914 fixed, 13, 10.393, 11.14, 0.933 fixed, 14, 10.628, 12.097, 0.879 fixed, 15, 10.982, 12.965, 0.847 fixed, 16, 11.851, 14.429, 0.821 fixed, 32, 24.334, 34.414, 0.707 fixed, 64, 55.618, 86.688, 0.642 fixed, 128, 118.261, 224.36, 0.527 fixed, 256, 256.183, 538.629, 0.476 random, 2, 11.194, 11.556, 0.969 random, 4, 17.516, 17.205, 1.018 random, 8, 23.501, 20.985, 1.12 random, 16, 28.131, 29.212, 0.963 random, 32, 35.436, 38.662, 0.917 random, 64, 45.74, 58.868, 0.777 random, 128, 75.394, 121.963, 0.618 random, 256, 139.524, 260.726, 0.535 --- nss/nss_hash.c | 79 +++++++++++++++++++++++++++----------------------- 1 file changed, 42 insertions(+), 37 deletions(-) diff --git a/nss/nss_hash.c b/nss/nss_hash.c index 27a348ea9b..c6a375f386 100644 --- a/nss/nss_hash.c +++ b/nss/nss_hash.c @@ -19,58 +19,63 @@ /* This is from libc/db/hash/hash_func.c, hash3 is static there */ /* - * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte + * This is INCREDIBLY ugly, but fast. We break the string up into 4 byte * units. On the first time through the loop we get the "leftover bytes" - * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle - * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If - * this routine is heavily used enough, it's worth the ugly coding. + * (len % 4). On every other iteration, we perform a 4x unrolled version + * HASHC. Further unrolling does not appear to help. * * OZ's original sdbm hash */ uint32_t __nss_hash (const void *keyarg, size_t len) { + enum + { + HASH_CONST_P0 = 1, /* (uint32_t)(65599 ^ 0). */ + HASH_CONST_P1 = 65599, /* (uint32_t)(65599 ^ 1). */ + HASH_CONST_P2 = 8261505, /* (uint32_t)(65599 ^ 2). */ + HASH_CONST_P3 = 780587199, /* (uint32_t)(65599 ^ 3). */ + HASH_CONST_P4 = 1139564289 /* (uint32_t)(65599 ^ 4). */ + }; + const unsigned char *key; - size_t loop; uint32_t h; -#define HASHC h = *key++ + 65599 * h +#define HASHC h = *key++ + HASH_CONST_P1 * h h = 0; key = keyarg; if (len > 0) { - loop = (len + 8 - 1) >> 3; - switch (len & (8 - 1)) - { - case 0: - do - { - HASHC; - /* FALLTHROUGH */ - case 7: - HASHC; - /* FALLTHROUGH */ - case 6: - HASHC; - /* FALLTHROUGH */ - case 5: - HASHC; - /* FALLTHROUGH */ - case 4: - HASHC; - /* FALLTHROUGH */ - case 3: - HASHC; - /* FALLTHROUGH */ - case 2: - HASHC; - /* FALLTHROUGH */ - case 1: - HASHC; - } - while (--loop); - } + switch ((len & (4 - 1))) + { + case 0: + /* h starts out as zero so no need to include the multiply. */ + h = *key++; + /* FALLTHROUGH */ + case 3: + HASHC; + /* FALLTHROUGH */ + case 2: + HASHC; + /* FALLTHROUGH */ + case 1: + HASHC; + /* FALLTHROUGH */ + } + + uint32_t c0, c1, c2, c3; + for (--len; len >= 4; len -= 4) + { + c0 = (unsigned char) *(key + 0); + c1 = (unsigned char) *(key + 1); + c2 = (unsigned char) *(key + 2); + c3 = (unsigned char) *(key + 3); + h = HASH_CONST_P4 * h + HASH_CONST_P3 * c0 + HASH_CONST_P2 * c1 + + HASH_CONST_P1 * c2 + HASH_CONST_P0 * c3; + + key += 4; + } } return h; } -- 2.25.1