From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264530AbUHNShi (ORCPT ); Sat, 14 Aug 2004 14:37:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264560AbUHNShh (ORCPT ); Sat, 14 Aug 2004 14:37:37 -0400 Received: from ozlabs.org ([203.10.76.45]:24992 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S264530AbUHNShI (ORCPT ); Sat, 14 Aug 2004 14:37:08 -0400 Date: Sun, 15 Aug 2004 04:36:23 +1000 From: Anton Blanchard To: Arnd Bergmann , akpm@osdl.org Cc: linux-kernel@vger.kernel.org, richm@oldelvet.org.uk, tytso@mit.edu Subject: Re: Using get_cycles for add_timer_randomness Message-ID: <20040814183623.GB5637@krispykreme> References: <200308160303.17612.arnd@arndb.de> <20040810162435.GK24690@krispykreme> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040810162435.GK24690@krispykreme> User-Agent: Mutt/1.5.6+20040803i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > This sounded like a good idea at the time, any reason we cant merge > this? Merged against latest bk. I tested how long it took to do a dd from /dev/random on ppc64 before and after this patch, while doing a ping flood from another machine. before: # /usr/bin/time dd if=/dev/random of=/dev/zero count=1k 0+51 records in Command terminated by signal 2 0.00user 0.00system 19:18.46elapsed 0%CPU (0avgtext+0avgdata 0maxresident)k I gave up after 19 minutes. after: # /usr/bin/time dd if=/dev/random of=/dev/zero count=1k 0+1024 records in 0.00user 0.00system 0:33.38elapsed 0%CPU (0avgtext+0avgdata 0maxresident)k Just over 33 seconds. Better. Anton -- From: Arnd Bergmann I noticed that only i386 and x86-64 are currently using a high resolution timer source when adding randomness. Since many architectures have a working get_cycles() implementation, it seems rather straightforward to use that. Has this been discussed before, or can anyone comment on the implementation below? This patch attempts to take into account the size of cycles_t, which is either 32 or 64 bits wide but independent of the architecture's word size. The behavior should be nearly identical to the old one on i386, x86-64 and all architectures without a time stamp counter, while finding more entropy on the other architectures. Signed-off-by: Anton Blanchard ===== drivers/char/random.c 1.45 vs edited ===== --- 1.45/drivers/char/random.c Sun Aug 8 16:43:40 2004 +++ edited/drivers/char/random.c Sun Aug 15 03:13:21 2004 @@ -781,8 +781,8 @@ /* There is one of these per entropy source */ struct timer_rand_state { - __u32 last_time; - __s32 last_delta,last_delta2; + cycles_t last_time; + long last_delta,last_delta2; int dont_count_entropy:1; }; @@ -799,14 +799,12 @@ * The number "num" is also added to the pool - it should somehow describe * the type of event which just happened. This is currently 0-255 for * keyboard scan codes, and 256 upwards for interrupts. - * On the i386, this is assumed to be at most 16 bits, and the high bits - * are used for a high-resolution timer. * */ static void add_timer_randomness(struct timer_rand_state *state, unsigned num) { - __u32 time; - __s32 delta, delta2, delta3; + cycles_t time; + long delta, delta2, delta3; int entropy = 0; /* if over the trickle threshold, use only 1 in 4096 samples */ @@ -814,17 +812,18 @@ (__get_cpu_var(trickle_count)++ & 0xfff)) return; -#if defined (__i386__) || defined (__x86_64__) - if (cpu_has_tsc) { - __u32 high; - rdtsc(time, high); - num ^= high; + /* + * Use get_cycles() if implemented, otherwise fall back to + * jiffies. + */ + time = get_cycles(); + if (time != 0) { + if (sizeof(time) > 4) { + num ^= (u32)(time >> 32); + } } else { time = jiffies; } -#else - time = jiffies; -#endif /* * Calculate number of bits of randomness we probably added. ===== include/asm-i386/timex.h 1.7 vs edited ===== --- 1.7/include/asm-i386/timex.h Fri Jun 18 16:43:58 2004 +++ edited/include/asm-i386/timex.h Sun Aug 15 02:41:55 2004 @@ -7,7 +7,7 @@ #define _ASMi386_TIMEX_H #include -#include +#include #ifdef CONFIG_X86_ELAN # define CLOCK_TICK_RATE 1189200 /* AMD Elan has different frequency! */ @@ -40,14 +40,17 @@ static inline cycles_t get_cycles (void) { + unsigned long long ret=0; + #ifndef CONFIG_X86_TSC - return 0; -#else - unsigned long long ret; + if (!cpu_has_tsc) + return 0; +#endif +#if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC) rdtscll(ret); - return ret; #endif + return ret; } extern unsigned long cpu_khz;