From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765374AbXHKAlj (ORCPT ); Fri, 10 Aug 2007 20:41:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757759AbXHKAlc (ORCPT ); Fri, 10 Aug 2007 20:41:32 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:59935 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757627AbXHKAlb (ORCPT ); Fri, 10 Aug 2007 20:41:31 -0400 Date: Fri, 10 Aug 2007 17:41:29 -0700 From: "Paul E. McKenney" To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, josht@linux.vnet.ibm.com, dipankar@in.ibm.com, bunk@kernel.org Subject: [PATCH] Make rcutorture RNG use locally grown entropy Message-ID: <20070811004129.GA26356@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This patch converts rcutorture's random-number generator from get_random_bytes() (which has locking issues in some builds with patches) to instead use local-to-rcutorture statistical counters. This involves reading other CPUs' statistics, so the frequency of entropy addition is simultaneously decreased by an order of magnitude. This patch is an alternative to adding an EXPORT_SYMBOL_GPL() for the new cpu_clock() API. Signed-off-by: Paul E. McKenney --- rcutorture.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff -urpNa -X dontdiff linux-2.6.22.1-rt4/kernel/rcutorture.c linux-2.6.22.1-rt4-rcutorturesched/kernel/rcutorture.c --- linux-2.6.22.1-rt4/kernel/rcutorture.c 2007-07-21 16:58:22.000000000 -0700 +++ linux-2.6.22.1-rt4-rcutorturesched/kernel/rcutorture.c 2007-08-10 08:42:41.000000000 -0700 @@ -155,26 +155,27 @@ rcu_torture_free(struct rcu_torture *p) struct rcu_random_state { unsigned long rrs_state; long rrs_count; + int rrs_cpu; }; #define RCU_RANDOM_MULT 39916801 /* prime */ #define RCU_RANDOM_ADD 479001701 /* prime */ -#define RCU_RANDOM_REFRESH 10000 +#define RCU_RANDOM_REFRESH 100000 #define DEFINE_RCU_RANDOM(name) struct rcu_random_state name = { 0, 0 } /* * Crude but fast random-number generator. Uses a linear congruential - * generator, with occasional help from get_random_bytes(). + * generator, with occasional help from other CPUs' fast-running statistics. */ static unsigned long rcu_random(struct rcu_random_state *rrsp) { - long refresh; - if (--rrsp->rrs_count < 0) { - get_random_bytes(&refresh, sizeof(refresh)); - rrsp->rrs_state += refresh; + rrsp->rrs_cpu = next_cpu(rrsp->rrs_cpu, cpu_online_map); + if (rrsp->rrs_cpu >= NR_CPUS) + rrsp->rrs_cpu = 0; + rrsp->rrs_state += per_cpu(rcu_torture_count, rrsp->rrs_cpu)[0]; rrsp->rrs_count = RCU_RANDOM_REFRESH; } rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;