From 0f41c0ddadfb3d5baffe62351c380e2881aacd58 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Mar 2015 18:33:20 -0700 Subject: rcu: Provide diagnostic option to slow down grace-period scans Grace-period scans of the rcu_node combining tree normally proceed quite quickly, so that it is very difficult to reproduce races against them. This commit therefore allows grace-period pre-initialization and cleanup to be artificially slowed down, increasing race-reproduction probability. A pair of pairs of new Kconfig parameters are provided, RCU_TORTURE_TEST_SLOW_PREINIT to enable the slowing down of propagating CPU-hotplug changes up the combining tree along with RCU_TORTURE_TEST_SLOW_PREINIT_DELAY to specify the delay in jiffies, and RCU_TORTURE_TEST_SLOW_CLEANUP to enable the slowing down of the end-of-grace-period cleanup scan along with RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY to specify the delay in jiffies. Boot-time parameters named rcutree.gp_preinit_delay and rcutree.gp_cleanup_delay allow these delays to be specified at boot time. Signed-off-by: Paul E. McKenney --- Documentation/kernel-parameters.txt | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'Documentation/kernel-parameters.txt') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 61ab1628a057..10a4fb80c033 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2992,11 +2992,23 @@ bytes respectively. Such letter suffixes can also be entirely omitted. Set maximum number of finished RCU callbacks to process in one batch. + rcutree.gp_cleanup_delay= [KNL] + Set the number of jiffies to delay each step of + RCU grace-period cleanup. This only has effect + when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set. + rcutree.gp_init_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period initialization. This only has - effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT is - set. + effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT + is set. + + rcutree.gp_preinit_delay= [KNL] + Set the number of jiffies to delay each step of + RCU grace-period pre-initialization, that is, + the propagation of recent CPU-hotplug changes up + the rcu_node combining tree. This only has effect + when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set. rcutree.rcu_fanout_leaf= [KNL] Increase the number of CPUs assigned to each -- cgit v1.2.3 From 7fa270010e0ddd3693381431f373b3e3135b0695 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 20 Apr 2015 10:27:15 -0700 Subject: rcu: Convert CONFIG_RCU_FANOUT_EXACT to boot parameter The CONFIG_RCU_FANOUT_EXACT Kconfig parameter is used primarily (and perhaps only) by rcutorture to verify that RCU works correctly in specific rcu_node combining-tree configurations. It therefore does not make much sense have this as a question to people attempting to configure their kernels. So this commit creates an rcutree.rcu_fanout_exact= boot parameter that rcutorture can use, and eliminates the original CONFIG_RCU_FANOUT_EXACT Kconfig parameter. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney Reviewed-by: Pranith Kumar --- Documentation/kernel-parameters.txt | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'Documentation/kernel-parameters.txt') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 10a4fb80c033..f5582dcdf80d 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3010,6 +3010,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. the rcu_node combining tree. This only has effect when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set. + rcutree.rcu_fanout_exact= [KNL] + Disable autobalancing of the rcu_node combining + tree. This is used by rcutorture, and might + possibly be useful for architectures having high + cache-to-cache transfer latencies. + rcutree.rcu_fanout_leaf= [KNL] Increase the number of CPUs assigned to each leaf rcu_node structure. Useful for very large -- cgit v1.2.3 From a3dc2948cec80f20a89e9b646d0c01b121e48e02 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 20 Apr 2015 11:40:50 -0700 Subject: rcu: Enable diagnostic dump of rcu_node combining tree The purpose of this commit is to make it easier to verify that RCU's combining tree is set up correctly, which is useful to have when making changes in how that tree is initialized. Signed-off-by: Paul E. McKenney Reviewed-by: Pranith Kumar [ paulmck: Fold fix found by Fengguang's 0-day test robot. ] --- Documentation/kernel-parameters.txt | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'Documentation/kernel-parameters.txt') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index f5582dcdf80d..a1cb88d9864e 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2992,6 +2992,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. Set maximum number of finished RCU callbacks to process in one batch. + rcutree.dump_tree= [KNL] + Dump the structure of the rcu_node combining tree + out at early boot. This is used for diagnostic + purposes, to verify correct tree setup. + rcutree.gp_cleanup_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period cleanup. This only has effect -- cgit v1.2.3 From 3838cc1850ccd09f93e729e9047ec1995026f83e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Mar 2015 13:55:48 -0700 Subject: rcutorture: Allow negative values of nreaders to oversubscribe By default, with rcutorture.nreaders equal to -1, rcutorture provisions N-1 reader kthreads, where N is the number of CPUs. This avoids rcutorture-induced stalls, but also avoids heavier levels of torture. This commit therefore allows negative values of rcutorture.nreaders to specify larger numbers of reader kthreads, so that for example rcutorture.nreaders=-2 provisions N kthreads and rcutorture.nreaders=-5 provisions N+3 kthreads. Signed-off-by: Paul E. McKenney [ paulmck: Update documentation, as suggested by Josh Triplett. ] --- Documentation/kernel-parameters.txt | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'Documentation/kernel-parameters.txt') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 61ab1628a057..04b811086dca 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3101,7 +3101,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. test, hence the "fake". rcutorture.nreaders= [KNL] - Set number of RCU readers. + Set number of RCU readers. The value -1 selects + N-1, where N is the number of CPUs. A value + "n" less than -1 selects N-n-2, where N is again + the number of CPUs. For example, -2 selects N + (the number of CPUs), -3 selects N+1, and so on. rcutorture.object_debug= [KNL] Enable debug-object double-call_rcu() testing. -- cgit v1.2.3