[PATCH] rcu: unify boost and kthread priorities

[PATCH] rcu: unify boost and kthread priorities

[Clark Williams]

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Paul,

Here's the result of our conversation Friday, regarding the per-CPU and
boost priorities:

Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
threads (rcub/n).

Also, create the module_parameter rcutree.kthread_prio to be used on
the kernel command line at boot to set a new value
(rcutree.kthread_prio=N).

Signed-off-by: Clark Williams <clark.williams@gmail.com>
---
 Documentation/kernel-parameters.txt |  6 ++++++
 init/Kconfig                        | 23 ++++++++++++-----------
 kernel/rcu/tree_plugin.h            | 16 ++++++++--------
 3 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt index 10d51c2f10d7..471f885ab24d
100644 --- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2856,6 +2856,12 @@ bytes respectively. Such letter suffixes can
also be entirely omitted. quiescent states.  Units are jiffies, minimum
 			value is one, and maximum value is HZ.
 
+	rcutree.kthread_prio= 	 [KNL,BOOT]
+			Set the SCHED_FIFO priority of the RCU
+			per-CPU kthreads (rcuc/N). This value is also
+			used for the priority of the RCU boost threads
+			(rcub/N). Valid values are 1-99.
+
 	rcutree.rcu_nocb_leader_stride= [KNL]
 			Set the number of NOCB kthread groups, which
 			defaults to the square root of the number of
diff --git a/init/Kconfig b/init/Kconfig
index e84c6423a2e5..beacc8bb1523 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -662,30 +662,31 @@ config RCU_BOOST
 	  Say Y here if you are working with real-time apps or heavy
loads Say N here if you are unsure.
 
-config RCU_BOOST_PRIO
-	int "Real-time priority to boost RCU readers to"
+config RCU_KTHREAD_PRIO
+	int "Real-time priority to use for RCU worker threads"
 	range 1 99
 	depends on RCU_BOOST
 	default 1
 	help
-	  This option specifies the real-time priority to which
long-term
-	  preempted RCU readers are to be boosted.  If you are working
-	  with a real-time application that has one or more CPU-bound
-	  threads running at a real-time priority level, you should set
-	  RCU_BOOST_PRIO to a priority higher then the highest-priority
-	  real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
-	  of 1 is appropriate in the common case, which is real-time
+	  This option specifies the SCHED_FIFO priority value that
will be
+	  assigned to the rcuc/n and rcub/n threads and is also the
value
+	  used for RCU_BOOST (if enabled). If you are working with a
+	  real-time application that has one or more CPU-bound threads
+	  running at a real-time priority level, you should set
+	  RCU_KTHREAD_PRIO to a priority higher than the
highest-priority
+	  real-time CPU-bound application thread.  The default
RCU_KTHREAD_PRIO
+	  value of 1 is appropriate in the common case, which is
real-time applications that do not have any CPU-bound threads.
 
 	  Some real-time applications might not have a single real-time
 	  thread that saturates a given CPU, but instead might have
 	  multiple real-time threads that, taken together, fully
utilize
-	  that CPU.  In this case, you should set RCU_BOOST_PRIO to
+	  that CPU.  In this case, you should set RCU_KTHREAD_PRIO to
 	  a priority higher than the lowest-priority thread that is
 	  conspiring to prevent the CPU from running any non-real-time
 	  tasks.  For example, if one thread at priority 10 and another
 	  thread at priority 5 are between themselves fully consuming
-	  the CPU time on a given CPU, then RCU_BOOST_PRIO should be
+	  the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
 	  set to priority 6 or higher.
 
 	  Specify the real-time priority, or take the default if
unsure. diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a7997e272564..dfb3b793b80a 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -30,13 +30,10 @@
 #include <linux/smpboot.h>
 #include "../time/tick-internal.h"
 
-#define RCU_KTHREAD_PRIO 1
-
 #ifdef CONFIG_RCU_BOOST
-#include "../locking/rtmutex_common.h"
-#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
-#else
-#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
+/* rcuc/rcub kthread realtime priority */
+static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
+module_param(kthread_prio, int, 0644);
 #endif
 
 #ifdef CONFIG_RCU_NOCB_CPU
@@ -112,6 +109,9 @@ static void __init rcu_bootup_announce_oddness(void)
 			pr_info("\tPoll for callbacks from no-CBs
CPUs.\n"); }
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
+#ifdef CONFIG_RCU_BOOST
+	pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
+#endif
 }
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
@@ -1352,7 +1352,7 @@ static int rcu_spawn_one_boost_kthread(struct
rcu_state *rsp, smp_mb__after_unlock_lock();
 	rnp->boost_kthread_task = t;
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
-	sp.sched_priority = RCU_BOOST_PRIO;
+	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
 	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
 	return 0;
@@ -1369,7 +1369,7 @@ static void rcu_cpu_kthread_setup(unsigned int
cpu) {
 	struct sched_param sp;
 
-	sp.sched_priority = RCU_KTHREAD_PRIO;
+	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
 }
 
-- 
1.9.3


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Re: [PATCH] rcu: unify boost and kthread priorities

[Paul E. McKenney]

On Mon, Sep 15, 2014 at 10:05:24AM -0500, Clark Williams wrote:
> Paul,
> 
> Here's the result of our conversation Friday, regarding the per-CPU and
> boost priorities:
> 
> Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
> value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
> threads (rcub/n).
> 
> Also, create the module_parameter rcutree.kthread_prio to be used on
> the kernel command line at boot to set a new value
> (rcutree.kthread_prio=N).
> 
> Signed-off-by: Clark Williams <clark.williams@gmail.com>

Thank you, Clark!

I queued this, porting to rcu/dev, which resulted in the following
patch.  Please check this to make sure it still reflects your intent.
In the meantime, I will start testing.

							Thanx, Paul

------------------------------------------------------------------------

rcu: unify boost and kthread priorities

Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
threads (rcub/n).

Also, create the module_parameter rcutree.kthread_prio to be used on
the kernel command line at boot to set a new value (rcutree.kthread_prio=N).

Signed-off-by: Clark Williams <clark.williams@gmail.com>
[ paulmck: Ported to rcu/dev. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e95b0f43229f..c40395720a6f 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2899,6 +2899,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			quiescent states.  Units are jiffies, minimum
 			value is one, and maximum value is HZ.
 
+	rcutree.kthread_prio= 	 [KNL,BOOT]
+			Set the SCHED_FIFO priority of the RCU
+			per-CPU kthreads (rcuc/N). This value is also
+			used for the priority of the RCU boost threads
+			(rcub/N). Valid values are 1-99.
+
 	rcutree.rcu_nocb_leader_stride= [KNL]
 			Set the number of NOCB kthread groups, which
 			defaults to the square root of the number of
diff --git a/init/Kconfig b/init/Kconfig
index 95a1447a33bd..8a2b97c4026a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -672,30 +672,31 @@ config RCU_BOOST
 	  Say Y here if you are working with real-time apps or heavy loads
 	  Say N here if you are unsure.
 
-config RCU_BOOST_PRIO
-	int "Real-time priority to boost RCU readers to"
+config RCU_KTHREAD_PRIO
+	int "Real-time priority to use for RCU worker threads"
 	range 1 99
 	depends on RCU_BOOST
 	default 1
 	help
-	  This option specifies the real-time priority to which long-term
-	  preempted RCU readers are to be boosted.  If you are working
-	  with a real-time application that has one or more CPU-bound
-	  threads running at a real-time priority level, you should set
-	  RCU_BOOST_PRIO to a priority higher then the highest-priority
-	  real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
-	  of 1 is appropriate in the common case, which is real-time
+	  This option specifies the SCHED_FIFO priority value that will be
+	  assigned to the rcuc/n and rcub/n threads and is also the value
+	  used for RCU_BOOST (if enabled). If you are working with a
+	  real-time application that has one or more CPU-bound threads
+	  running at a real-time priority level, you should set
+	  RCU_KTHREAD_PRIO to a priority higher than the highest-priority
+	  real-time CPU-bound application thread.  The default RCU_KTHREAD_PRIO
+	  value of 1 is appropriate in the common case, which is real-time
 	  applications that do not have any CPU-bound threads.
 
 	  Some real-time applications might not have a single real-time
 	  thread that saturates a given CPU, but instead might have
 	  multiple real-time threads that, taken together, fully utilize
-	  that CPU.  In this case, you should set RCU_BOOST_PRIO to
+	  that CPU.  In this case, you should set RCU_KTHREAD_PRIO to
 	  a priority higher than the lowest-priority thread that is
 	  conspiring to prevent the CPU from running any non-real-time
 	  tasks.  For example, if one thread at priority 10 and another
 	  thread at priority 5 are between themselves fully consuming
-	  the CPU time on a given CPU, then RCU_BOOST_PRIO should be
+	  the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
 	  set to priority 6 or higher.
 
 	  Specify the real-time priority, or take the default if unsure.
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index cbd08fc4b706..77f9376f3f8d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -30,12 +30,13 @@
 #include <linux/smpboot.h>
 #include "../time/tick-internal.h"
 
-#define RCU_KTHREAD_PRIO 1
-
 #ifdef CONFIG_RCU_BOOST
 
 #include "../locking/rtmutex_common.h"
-#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
+
+/* rcuc/rcub kthread realtime priority */
+static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
+module_param(kthread_prio, int, 0644);
 
 /*
  * Control variables for per-CPU and per-rcu_node kthreads.  These
@@ -46,11 +47,7 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 DEFINE_PER_CPU(char, rcu_cpu_has_work);
 
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
-
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
+#endif /* #ifdef CONFIG_RCU_BOOST */
 
 #ifdef CONFIG_RCU_NOCB_CPU
 static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
@@ -95,6 +92,9 @@ static void __init rcu_bootup_announce_oddness(void)
 		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
 	if (nr_cpu_ids != NR_CPUS)
 		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
+#ifdef CONFIG_RCU_BOOST
+	pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
+#endif
 }
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
@@ -1326,7 +1326,7 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
 	smp_mb__after_unlock_lock();
 	rnp->boost_kthread_task = t;
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
-	sp.sched_priority = RCU_BOOST_PRIO;
+	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
 	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
 	return 0;
@@ -1343,7 +1343,7 @@ static void rcu_cpu_kthread_setup(unsigned int cpu)
 {
 	struct sched_param sp;
 
-	sp.sched_priority = RCU_KTHREAD_PRIO;
+	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
 }
 

Re: [PATCH] rcu: unify boost and kthread priorities

[Clark Williams]

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On Tue, 16 Sep 2014 13:41:56 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> On Mon, Sep 15, 2014 at 10:05:24AM -0500, Clark Williams wrote:
> > Paul,
> > 
> > Here's the result of our conversation Friday, regarding the per-CPU and
> > boost priorities:
> > 
> > Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
> > value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
> > threads (rcub/n).
> > 
> > Also, create the module_parameter rcutree.kthread_prio to be used on
> > the kernel command line at boot to set a new value
> > (rcutree.kthread_prio=N).
> > 
> > Signed-off-by: Clark Williams <clark.williams@gmail.com>
> 
> Thank you, Clark!
> 
> I queued this, porting to rcu/dev, which resulted in the following
> patch.  Please check this to make sure it still reflects your intent.
> In the meantime, I will start testing.
> 
> 							Thanx, Paul

Yes, looks right (and you fixed that I didn't have it all under
RCU_BOOST). 

Thanks,
Clark

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Re: [PATCH] rcu: unify boost and kthread priorities

[Paul E. McKenney]

On Wed, Sep 17, 2014 at 08:14:42AM -0500, Clark Williams wrote:
> On Tue, 16 Sep 2014 13:41:56 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> 
> > On Mon, Sep 15, 2014 at 10:05:24AM -0500, Clark Williams wrote:
> > > Paul,
> > > 
> > > Here's the result of our conversation Friday, regarding the per-CPU and
> > > boost priorities:
> > > 
> > > Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
> > > value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
> > > threads (rcub/n).
> > > 
> > > Also, create the module_parameter rcutree.kthread_prio to be used on
> > > the kernel command line at boot to set a new value
> > > (rcutree.kthread_prio=N).
> > > 
> > > Signed-off-by: Clark Williams <clark.williams@gmail.com>
> > 
> > Thank you, Clark!
> > 
> > I queued this, porting to rcu/dev, which resulted in the following
> > patch.  Please check this to make sure it still reflects your intent.
> > In the meantime, I will start testing.
> > 
> > 							Thanx, Paul
> 
> Yes, looks right (and you fixed that I didn't have it all under
> RCU_BOOST). 

Very good!  Early testing looks good, will let you know how it goes.

							Thanx, Paul

Re: [PATCH] rcu: unify boost and kthread priorities

[Paul Bolle]

Hi Paul,

On Tue, 2014-09-16 at 13:41 -0700, Paul E. McKenney wrote:
> rcu: unify boost and kthread priorities
> 
> Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
> value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
> threads (rcub/n).
> 
> Also, create the module_parameter rcutree.kthread_prio to be used on
> the kernel command line at boot to set a new value (rcutree.kthread_prio=N).
> 
> Signed-off-by: Clark Williams <clark.williams@gmail.com>
> [ paulmck: Ported to rcu/dev. ]
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

This landed in today's linux-next (ie, next-20140917) as commit
04a96e05bda6 ("rcu: unify boost and kthread priorities").

> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>[...]
> diff --git a/init/Kconfig b/init/Kconfig
>[...]
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
>[...]

There's a reference to CONFIG_RCU_BOOST_PRIO in
tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt. It needs
updating too, doesn't it?


Paul Bolle

Re: [PATCH] rcu: unify boost and kthread priorities

[Paul E. McKenney]

On Wed, Sep 17, 2014 at 06:49:03PM +0200, Paul Bolle wrote:
> Hi Paul,
> 
> On Tue, 2014-09-16 at 13:41 -0700, Paul E. McKenney wrote:
> > rcu: unify boost and kthread priorities
> > 
> > Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
> > value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
> > threads (rcub/n).
> > 
> > Also, create the module_parameter rcutree.kthread_prio to be used on
> > the kernel command line at boot to set a new value (rcutree.kthread_prio=N).
> > 
> > Signed-off-by: Clark Williams <clark.williams@gmail.com>
> > [ paulmck: Ported to rcu/dev. ]
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> This landed in today's linux-next (ie, next-20140917) as commit
> 04a96e05bda6 ("rcu: unify boost and kthread priorities").
> 
> > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> >[...]
> > diff --git a/init/Kconfig b/init/Kconfig
> >[...]
> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> >[...]
> 
> There's a reference to CONFIG_RCU_BOOST_PRIO in
> tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt. It needs
> updating too, doesn't it?

Good catch!

Also the one in tools/testing/selftests/rcutorture/configs/rcu/TREE03.

Fixed both, thank you!

							Thanx, Paul

Re: [PATCH] rcu: unify boost and kthread priorities

[Paul Bolle]

On Wed, 2014-09-17 at 10:17 -0700, Paul E. McKenney wrote:
> On Wed, Sep 17, 2014 at 06:49:03PM +0200, Paul Bolle wrote:
> > There's a reference to CONFIG_RCU_BOOST_PRIO in
> > tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt. It needs
> > updating too, doesn't it?
> 
> Good catch!
> 
> Also the one in tools/testing/selftests/rcutorture/configs/rcu/TREE03.

>From my local perl monstrosity:
	# ...  and Paul McKenney's rcutorture stuff (v3.14-rc+)
	if ($blob->[1] =~ /tools\/testing\/selftests\/rcutorture\/configs\/.*/) {

Ie, I've made that script ignore all references to Kconfig macros below
tools/testing/selftest/rcutorture/configs. Is that too crude?

> Fixed both, thank you!


Paul Bolle

Re: [PATCH] rcu: unify boost and kthread priorities

[Paul E. McKenney]

On Wed, Sep 17, 2014 at 07:45:57PM +0200, Paul Bolle wrote:
> On Wed, 2014-09-17 at 10:17 -0700, Paul E. McKenney wrote:
> > On Wed, Sep 17, 2014 at 06:49:03PM +0200, Paul Bolle wrote:
> > > There's a reference to CONFIG_RCU_BOOST_PRIO in
> > > tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt. It needs
> > > updating too, doesn't it?
> > 
> > Good catch!
> > 
> > Also the one in tools/testing/selftests/rcutorture/configs/rcu/TREE03.
> 
> >From my local perl monstrosity:
> 	# ...  and Paul McKenney's rcutorture stuff (v3.14-rc+)
> 	if ($blob->[1] =~ /tools\/testing\/selftests\/rcutorture\/configs\/.*/) {
> 
> Ie, I've made that script ignore all references to Kconfig macros below
> tools/testing/selftest/rcutorture/configs. Is that too crude?

It would not hurt to check the files that appear in the CFLIST files:

	tools/testing/selftests/rcutorture/configs/lock/CFLIST
	tools/testing/selftests/rcutorture/configs/rcu/CFLIST

These files drive the torture-test kernel configurations.

That said, yes, there are sometimes some obsolete or deprecated
Kconfig parameters in these files because some systems need them.

							Thanx, Paul

> > Fixed both, thank you!
> 
> 
> Paul Bolle
>