Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753454Ab3IVUk5 (ORCPT ); Sun, 22 Sep 2013 16:40:57 -0400 Received: from imap.thunk.org ([74.207.234.97]:35976 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752669Ab3IVUjS (ORCPT ); Sun, 22 Sep 2013 16:39:18 -0400 From: "Theodore Ts'o" To: Linux Kernel Developers List Cc: hpa@zytor.com, joern@logfs.org, macro@linux-mips.org, ralf@linux-mips.org, dave.taht@gmail.com, blogic@openwrt.org, andrewmcgr@gmail.com, smueller@chronox.de, geert@linux-m68k.org, tg@mirbsd.de, "H. Peter Anvin" , , "Theodore Ts'o" Subject: [PATCH, RFC 02/12] random: Statically compute poolbitshift, poolbytes, poolbits Date: Sun, 22 Sep 2013 16:38:48 -0400 Message-Id: <1379882338-7209-3-git-send-email-tytso@mit.edu> X-Mailer: git-send-email 1.7.12.rc0.22.gcdd159b In-Reply-To: <1379882338-7209-1-git-send-email-tytso@mit.edu> References: <1379882338-7209-1-git-send-email-tytso@mit.edu> X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4695 Lines: 129 From: "H. Peter Anvin" Use a macro to statically compute poolbitshift (will be used in a subsequent patch), poolbytes, and poolbits. On virtually all architectures the cost of a memory load with an offset is the same as the one of a memory load. It is still possible for this to generate worse code since the C compiler doesn't know the fixed relationship between these fields, but that is somewhat unlikely. Signed-off-by: H. Peter Anvin Cc: Signed-off-by: Theodore Ts'o --- drivers/char/random.c | 39 +++++++++++++++++++-------------------- 1 file changed, 19 insertions(+), 20 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 92e6c67..e973658 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -309,46 +309,45 @@ static DEFINE_PER_CPU(int, trickle_count); * scaled squared error sum) except for the last tap, which is 1 to * get the twisting happening as fast as possible. */ + static struct poolinfo { - int poolwords; + int poolbitshift, poolwords, poolbytes, poolbits; +#define S(x) ilog2(x)+5, (x), (x)*4, (x)*32 int tap1, tap2, tap3, tap4, tap5; } poolinfo_table[] = { /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */ - { 128, 103, 76, 51, 25, 1 }, + { S(128), 103, 76, 51, 25, 1 }, /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */ - { 32, 26, 20, 14, 7, 1 }, + { S(32), 26, 20, 14, 7, 1 }, #if 0 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */ - { 2048, 1638, 1231, 819, 411, 1 }, + { S(2048), 1638, 1231, 819, 411, 1 }, /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */ - { 1024, 817, 615, 412, 204, 1 }, + { S(1024), 817, 615, 412, 204, 1 }, /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */ - { 1024, 819, 616, 410, 207, 2 }, + { S(1024), 819, 616, 410, 207, 2 }, /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */ - { 512, 411, 308, 208, 104, 1 }, + { S(512), 411, 308, 208, 104, 1 }, /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */ - { 512, 409, 307, 206, 102, 2 }, + { S(512), 409, 307, 206, 102, 2 }, /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */ - { 512, 409, 309, 205, 103, 2 }, + { S(512), 409, 309, 205, 103, 2 }, /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */ - { 256, 205, 155, 101, 52, 1 }, + { S(256), 205, 155, 101, 52, 1 }, /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */ - { 128, 103, 78, 51, 27, 2 }, + { S(128), 103, 78, 51, 27, 2 }, /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */ - { 64, 52, 39, 26, 14, 1 }, + { S(64), 52, 39, 26, 14, 1 }, #endif }; -#define POOLBITS poolwords*32 -#define POOLBYTES poolwords*4 - /* * For the purposes of better mixing, we use the CRC-32 polynomial as * well to make a twisted Generalized Feedback Shift Reigster @@ -599,8 +598,8 @@ retry: if (entropy_count < 0) { DEBUG_ENT("negative entropy/overflow\n"); entropy_count = 0; - } else if (entropy_count > r->poolinfo->POOLBITS) - entropy_count = r->poolinfo->POOLBITS; + } else if (entropy_count > r->poolinfo->poolbits) + entropy_count = r->poolinfo->poolbits; if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) goto retry; @@ -815,7 +814,7 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes) __u32 tmp[OUTPUT_POOL_WORDS]; if (r->pull && r->entropy_count < nbytes * 8 && - r->entropy_count < r->poolinfo->POOLBITS) { + r->entropy_count < r->poolinfo->poolbits) { /* If we're limited, always leave two wakeup worth's BITS */ int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4; int bytes = nbytes; @@ -857,7 +856,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, /* Hold lock while accounting */ spin_lock_irqsave(&r->lock, flags); - BUG_ON(r->entropy_count > r->poolinfo->POOLBITS); + BUG_ON(r->entropy_count > r->poolinfo->poolbits); DEBUG_ENT("trying to extract %zu bits from %s\n", nbytes * 8, r->name); @@ -1112,7 +1111,7 @@ static void init_std_data(struct entropy_store *r) r->entropy_total = 0; r->last_data_init = false; mix_pool_bytes(r, &now, sizeof(now), NULL); - for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) { + for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) { if (!arch_get_random_long(&rv)) break; mix_pool_bytes(r, &rv, sizeof(rv), NULL); -- 1.7.12.rc0.22.gcdd159b -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/