[PATCH 2/3] sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default

[PATCH 2/3] sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default

[Frederic Weisbecker]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

The "isolcpus=" boot parameter support was always built-in before we
moved the related code under CONFIG_CPU_ISOLATION. Having it disabled by
default is very confusing for people accustomed to use this parameter.

So enable it by dafault to keep the previous behaviour but keep it
optable for those who want to tinify their kernels.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
---
 init/Kconfig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 2934249..690a381 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -461,10 +461,14 @@ endmenu # "CPU/Task time and stats accounting"
 
 config CPU_ISOLATION
 	bool "CPU isolation"
+	default y
 	help
 	  Make sure that CPUs running critical tasks are not disturbed by
 	  any source of "noise" such as unbound workqueues, timers, kthreads...
-	  Unbound jobs get offloaded to housekeeping CPUs.
+	  Unbound jobs get offloaded to housekeeping CPUs. This is driven by
+	  the "isolcpus=" boot parameter.
+
+	  Say Y if unsure.
 
 source "kernel/rcu/Kconfig"
 
-- 
2.7.4

[GIT PULL] Nohz and isolation fixes v2

[Frederic Weisbecker]

Ingo,

Please pull the nohz/fixes-v2 branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	nohz/fixes-v2

HEAD: 5ecdec22346b99967e8b4e8d78a5b4d23bf216f9

Thanks,
	Frederic
---

Frederic Weisbecker (2):
      sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default
      sched/isolation: Document boot parameters dependency on CONFIG_CPU_ISOLATION

Paul E. McKenney (1):
      sched/isolation: Make NO_HZ_FULL select CPU_ISOLATION


 Documentation/admin-guide/kernel-parameters.rst | 1 +
 Documentation/admin-guide/kernel-parameters.txt | 4 ++--
 init/Kconfig                                    | 6 +++++-
 kernel/time/Kconfig                             | 1 +
 4 files changed, 9 insertions(+), 3 deletions(-)

[PATCH 1/3] sched/isolation: Make NO_HZ_FULL select CPU_ISOLATION

[Frederic Weisbecker]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

CONFIG_NO_HZ_FULL doesn't make sense without CONFIG_CPU_ISOLATION. In
fact enabling the first without the second is a regression as nohz_full=
boot parameter gets silently ignored.

Besides this unnatural combination hangs RCU gp kthread when running
rcutorture for reasons that are not yet fully understood:

	rcu_preempt kthread starved for 9974 jiffies! g4294967208
	+c4294967207 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=0
	rcu_preempt     I 7464     8      2 0x80000000
	Call Trace:
		__schedule+0x493/0x620
		schedule+0x24/0x40
		schedule_timeout+0x330/0x3b0
		? preempt_count_sub+0xea/0x140
		? collect_expired_timers+0xb0/0xb0
		rcu_gp_kthread+0x6bf/0xef0

This commit therefore makes NO_HZ_FULL select CPU_ISOLATION, which
prevents all these bad behaviours.

Fixes: 5c4991e24c69 ("sched/isolation: Split out new CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL")

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/time/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index e776fc8..f6b5f19 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -95,6 +95,7 @@ config NO_HZ_FULL
 	select RCU_NOCB_CPU
 	select VIRT_CPU_ACCOUNTING_GEN
 	select IRQ_WORK
+	select CPU_ISOLATION
 	help
 	 Adaptively try to shutdown the tick whenever possible, even when
 	 the CPU is running tasks. Typically this requires running a single
-- 
2.7.4

[PATCH 2/3] sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default

[Frederic Weisbecker]

The "isolcpus=" boot parameter support was always built-in before we
moved the related code under CONFIG_CPU_ISOLATION. Having it disabled by
default is very confusing for people accustomed to use this parameter.

So enable it by dafault to keep the previous behaviour but keep it
optable for those who want to tinify their kernels.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
---
 init/Kconfig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 2934249..690a381 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -461,10 +461,14 @@ endmenu # "CPU/Task time and stats accounting"
 
 config CPU_ISOLATION
 	bool "CPU isolation"
+	default y
 	help
 	  Make sure that CPUs running critical tasks are not disturbed by
 	  any source of "noise" such as unbound workqueues, timers, kthreads...
-	  Unbound jobs get offloaded to housekeeping CPUs.
+	  Unbound jobs get offloaded to housekeeping CPUs. This is driven by
+	  the "isolcpus=" boot parameter.
+
+	  Say Y if unsure.
 
 source "kernel/rcu/Kconfig"
 
-- 
2.7.4

[PATCH 3/3] sched/isolation: Document boot parameters dependency on CONFIG_CPU_ISOLATION

[Frederic Weisbecker]

The "isolcpus=" and "nohz_full=" boot parameters depend on CPU Isolation
support. Let's document that.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
---
 Documentation/admin-guide/kernel-parameters.rst | 1 +
 Documentation/admin-guide/kernel-parameters.txt | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index b2598cc..7242cbd 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -109,6 +109,7 @@ parameter is applicable::
 	IPV6	IPv6 support is enabled.
 	ISAPNP	ISA PnP code is enabled.
 	ISDN	Appropriate ISDN support is enabled.
+	ISOL	CPU Isolation is enabled.
 	JOY	Appropriate joystick support is enabled.
 	KGDB	Kernel debugger support is enabled.
 	KVM	Kernel Virtual Machine support is enabled.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6571fbf..1683107 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1737,7 +1737,7 @@
 	isapnp=		[ISAPNP]
 			Format: <RDP>,<reset>,<pci_scan>,<verbosity>
 
-	isolcpus=	[KNL,SMP] Isolate a given set of CPUs from disturbance.
+	isolcpus=	[KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
 			[Deprecated - use cpusets instead]
 			Format: [flag-list,]<cpu-list>
 
@@ -2662,7 +2662,7 @@
 			Valid arguments: on, off
 			Default: on
 
-	nohz_full=	[KNL,BOOT]
+	nohz_full=	[KNL,BOOT,SMP,ISOL]
 			The argument is a cpu list, as described above.
 			In kernels built with CONFIG_NO_HZ_FULL=y, set
 			the specified list of CPUs whose tick will be stopped
-- 
2.7.4

[tip:sched/urgent] sched/isolation: Make CONFIG_NO_HZ_FULL select CONFIG_CPU_ISOLATION

[tip-bot for Paul E. McKenney]

Commit-ID:  bf29cb238dc0656e6564b6a94bb82e11d2129437
Gitweb:     https://git.kernel.org/tip/bf29cb238dc0656e6564b6a94bb82e11d2129437
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Thu, 14 Dec 2017 19:18:25 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 18 Dec 2017 13:46:42 +0100

sched/isolation: Make CONFIG_NO_HZ_FULL select CONFIG_CPU_ISOLATION

CONFIG_NO_HZ_FULL doesn't make sense without CONFIG_CPU_ISOLATION. In
fact enabling the first without the second is a regression as nohz_full=
boot parameter gets silently ignored.

Besides this unnatural combination hangs RCU gp kthread when running
rcutorture for reasons that are not yet fully understood:

	rcu_preempt kthread starved for 9974 jiffies! g4294967208
	+c4294967207 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=0
	rcu_preempt     I 7464     8      2 0x80000000
	Call Trace:
		__schedule+0x493/0x620
		schedule+0x24/0x40
		schedule_timeout+0x330/0x3b0
		? preempt_count_sub+0xea/0x140
		? collect_expired_timers+0xb0/0xb0
		rcu_gp_kthread+0x6bf/0xef0

This commit therefore makes NO_HZ_FULL select CPU_ISOLATION, which
prevents all these bad behaviours.

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Fixes: 5c4991e24c69 ("sched/isolation: Split out new CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL")
Link: http://lkml.kernel.org/r/1513275507-29200-2-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/time/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index e776fc8..f6b5f19 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -95,6 +95,7 @@ config NO_HZ_FULL
 	select RCU_NOCB_CPU
 	select VIRT_CPU_ACCOUNTING_GEN
 	select IRQ_WORK
+	select CPU_ISOLATION
 	help
 	 Adaptively try to shutdown the tick whenever possible, even when
 	 the CPU is running tasks. Typically this requires running a single

[tip:sched/urgent] sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default

[tip-bot for Frederic Weisbecker]

Commit-ID:  2c43838c99d9d23f17eb2bdadafcb2879cca6995
Gitweb:     https://git.kernel.org/tip/2c43838c99d9d23f17eb2bdadafcb2879cca6995
Author:     Frederic Weisbecker <frederic@kernel.org>
AuthorDate: Thu, 14 Dec 2017 19:18:26 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 18 Dec 2017 13:46:42 +0100

sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default

The "isolcpus=" boot parameter support was always built-in before we
moved the related code under CONFIG_CPU_ISOLATION. Having it disabled by
default is very confusing for people accustomed to use this parameter.

So enable it by dafault to keep the previous behaviour but keep it
optable for those who want to tinify their kernels.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: kernel test robot <xiaolong.ye@intel.com>
Link: http://lkml.kernel.org/r/1513275507-29200-3-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 init/Kconfig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 2934249..690a381 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -461,10 +461,14 @@ endmenu # "CPU/Task time and stats accounting"
 
 config CPU_ISOLATION
 	bool "CPU isolation"
+	default y
 	help
 	  Make sure that CPUs running critical tasks are not disturbed by
 	  any source of "noise" such as unbound workqueues, timers, kthreads...
-	  Unbound jobs get offloaded to housekeeping CPUs.
+	  Unbound jobs get offloaded to housekeeping CPUs. This is driven by
+	  the "isolcpus=" boot parameter.
+
+	  Say Y if unsure.
 
 source "kernel/rcu/Kconfig"
 

[tip:sched/urgent] sched/isolation: Document boot parameters dependency on CONFIG_CPU_ISOLATION=y

[tip-bot for Frederic Weisbecker]

Commit-ID:  d94d105329e4a8a874853b5bd854b6587c41adda
Gitweb:     https://git.kernel.org/tip/d94d105329e4a8a874853b5bd854b6587c41adda
Author:     Frederic Weisbecker <frederic@kernel.org>
AuthorDate: Thu, 14 Dec 2017 19:18:27 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 18 Dec 2017 13:46:42 +0100

sched/isolation: Document boot parameters dependency on CONFIG_CPU_ISOLATION=y

The "isolcpus=" and "nohz_full=" boot parameters depend on CPU Isolation
support. Let's document that.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: kernel test robot <xiaolong.ye@intel.com>
Link: http://lkml.kernel.org/r/1513275507-29200-4-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.rst | 1 +
 Documentation/admin-guide/kernel-parameters.txt | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index b2598cc..7242cbd 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -109,6 +109,7 @@ parameter is applicable::
 	IPV6	IPv6 support is enabled.
 	ISAPNP	ISA PnP code is enabled.
 	ISDN	Appropriate ISDN support is enabled.
+	ISOL	CPU Isolation is enabled.
 	JOY	Appropriate joystick support is enabled.
 	KGDB	Kernel debugger support is enabled.
 	KVM	Kernel Virtual Machine support is enabled.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6571fbf..1683107 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1737,7 +1737,7 @@
 	isapnp=		[ISAPNP]
 			Format: <RDP>,<reset>,<pci_scan>,<verbosity>
 
-	isolcpus=	[KNL,SMP] Isolate a given set of CPUs from disturbance.
+	isolcpus=	[KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
 			[Deprecated - use cpusets instead]
 			Format: [flag-list,]<cpu-list>
 
@@ -2662,7 +2662,7 @@
 			Valid arguments: on, off
 			Default: on
 
-	nohz_full=	[KNL,BOOT]
+	nohz_full=	[KNL,BOOT,SMP,ISOL]
 			The argument is a cpu list, as described above.
 			In kernels built with CONFIG_NO_HZ_FULL=y, set
 			the specified list of CPUs whose tick will be stopped