[PATCH 0/3] nohz full: drop 64-bit requirement, enable ARM support v2

[PATCH 0/3] nohz full: drop 64-bit requirement, enable ARM support v2

[Frederic Weisbecker]

Hi Kevin,

Your patchset was fine but I just did a second round. Namely I did the following changes:

* Drop the 64 bits dependency after we settle the new dependency on HAVE_VIRT_CPU_ACCOUNTING_GEN
and not before. This way we don't have a middle state that loose the dependency in the middle of
the patchset. Probablyt no big deal but it looks more natural this way.

* Refined a few changelogs.

If you're ok I'll send a pull request to Ingo.

Thanks.

Kevin Hilman (3):
  vtime: Add HAVE_VIRT_CPU_ACCOUNTING_GEN Kconfig
  nohz: Drop generic vtime obsolete dependency on CONFIG_64BIT
  ARM: Kconfig: allow full nohz CPU accounting

 arch/Kconfig        | 12 ++++++++++++
 arch/arm/Kconfig    |  1 +
 init/Kconfig        |  3 ++-
 kernel/time/Kconfig |  2 +-
 4 files changed, 16 insertions(+), 2 deletions(-)

-- 
1.8.3.1

[PATCH 1/3] vtime: Add HAVE_VIRT_CPU_ACCOUNTING_GEN Kconfig

[Frederic Weisbecker]

From: Kevin Hilman <khilman@linaro.org>

With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit. In order
to use that feature, arch code should be audited to ensure there are no
races in concurrent read/write of cputime_t. For example,
reading/writing 64-bit cputime_t on some 32-bit arches may require
multiple accesses for low and high value parts, so proper locking
is needed to protect against concurrent accesses.

Therefore, add CONFIG_HAVE_VIRT_CPU_ACCOUNTING_GEN which arches can
enable after they've been audited for potential races.

This option is automatically enabled on 64-bit platforms.

Feature requested by Frederic Weisbecker.

Signed-off-by: Kevin Hilman <khilman@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Arm Linux <linux-arm-kernel@lists.infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 arch/Kconfig        | 12 ++++++++++++
 init/Kconfig        |  1 +
 kernel/time/Kconfig |  1 +
 3 files changed, 14 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index af2cc6e..185f8b0 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -353,6 +353,18 @@ config HAVE_CONTEXT_TRACKING
 config HAVE_VIRT_CPU_ACCOUNTING
 	bool
 
+config HAVE_VIRT_CPU_ACCOUNTING_GEN
+	bool
+	default y if 64BIT
+	help
+	  With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
+	  Before enabling this option, arch code must be audited
+	  to ensure there are no races in concurrent read/write of
+	  cputime_t. For example, reading/writing 64-bit cputime_t on
+	  some 32-bit arches may require multiple accesses, so proper
+	  locking is needed to protect against concurrent accesses.
+
+
 config HAVE_IRQ_TIME_ACCOUNTING
 	bool
 	help
diff --git a/init/Kconfig b/init/Kconfig
index 3ecd8a1..68c1a0e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -355,6 +355,7 @@ config VIRT_CPU_ACCOUNTING_NATIVE
 config VIRT_CPU_ACCOUNTING_GEN
 	bool "Full dynticks CPU time accounting"
 	depends on HAVE_CONTEXT_TRACKING && 64BIT
+	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select VIRT_CPU_ACCOUNTING
 	select CONTEXT_TRACKING
 	help
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 2b62fe8..f148475 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -101,6 +101,7 @@ config NO_HZ_FULL
 	depends on HAVE_CONTEXT_TRACKING
 	# VIRT_CPU_ACCOUNTING_GEN dependency
 	depends on 64BIT
+	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select NO_HZ_COMMON
 	select RCU_USER_QS
 	select RCU_NOCB_CPU
-- 
1.8.3.1

[PATCH 2/3] nohz: Drop generic vtime obsolete dependency on CONFIG_64BIT

[Frederic Weisbecker]

From: Kevin Hilman <khilman@linaro.org>

The CONFIG_64BIT requirement on vtime can finally be removed
since we now depend on HAVE_VIRT_CPU_ACCOUNTING_GEN which
already takes care of the arch ability to handle nsecs based
cputime_t safely.

Signed-off-by: Kevin Hilman <khilman@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Arm Linux <linux-arm-kernel@lists.infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 init/Kconfig        | 2 +-
 kernel/time/Kconfig | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 68c1a0e..841e79c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -354,7 +354,7 @@ config VIRT_CPU_ACCOUNTING_NATIVE
 
 config VIRT_CPU_ACCOUNTING_GEN
 	bool "Full dynticks CPU time accounting"
-	depends on HAVE_CONTEXT_TRACKING && 64BIT
+	depends on HAVE_CONTEXT_TRACKING
 	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select VIRT_CPU_ACCOUNTING
 	select CONTEXT_TRACKING
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index f148475..3ce6e8c 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -100,7 +100,6 @@ config NO_HZ_FULL
 	# RCU_USER_QS dependency
 	depends on HAVE_CONTEXT_TRACKING
 	# VIRT_CPU_ACCOUNTING_GEN dependency
-	depends on 64BIT
 	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select NO_HZ_COMMON
 	select RCU_USER_QS
-- 
1.8.3.1

[PATCH 3/3] ARM: Kconfig: allow full nohz CPU accounting

[Frederic Weisbecker]

From: Kevin Hilman <khilman@linaro.org>

With the 64-bit requirement removed from VIRT_CPU_ACCOUNTING_GEN,
allow ARM platforms to enable it.  Since VIRT_CPU_ACCOUNTING_GEN is a
dependency for full NO_HZ, this allows ARM platforms to enable full
NO_HZ as well.

Signed-off-by: Kevin Hilman <khilman@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Arm Linux <linux-arm-kernel@lists.infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 arch/arm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 1ad6fb6..323baf0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -54,6 +54,7 @@ config ARM
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UID16
+	select HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select IRQ_FORCED_THREADING
 	select KTIME_SCALAR
 	select MODULES_USE_ELF_REL
-- 
1.8.3.1

[PATCH 0/3] nohz full: drop 64-bit requirement, enable ARM support v2

[Kevin Hilman]

Frederic Weisbecker <fweisbec@gmail.com> writes:

> Hi Kevin,
>
> Your patchset was fine but I just did a second round. Namely I did the following changes:
>
> * Drop the 64 bits dependency after we settle the new dependency on HAVE_VIRT_CPU_ACCOUNTING_GEN
> and not before. This way we don't have a middle state that loose the dependency in the middle of
> the patchset. Probablyt no big deal but it looks more natural this way.
>
> * Refined a few changelogs.
>
> If you're ok I'll send a pull request to Ingo.

Looks good to me, thanks.

Kevin

> Kevin Hilman (3):
>   vtime: Add HAVE_VIRT_CPU_ACCOUNTING_GEN Kconfig
>   nohz: Drop generic vtime obsolete dependency on CONFIG_64BIT
>   ARM: Kconfig: allow full nohz CPU accounting
>
>  arch/Kconfig        | 12 ++++++++++++
>  arch/arm/Kconfig    |  1 +
>  init/Kconfig        |  3 ++-
>  kernel/time/Kconfig |  2 +-
>  4 files changed, 16 insertions(+), 2 deletions(-)

[PATCH 2/3] nohz: Drop generic vtime obsolete dependency on CONFIG_64BIT

[Ingo Molnar]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

>  config VIRT_CPU_ACCOUNTING_GEN
>  	bool "Full dynticks CPU time accounting"
> -	depends on HAVE_CONTEXT_TRACKING && 64BIT
> +	depends on HAVE_CONTEXT_TRACKING
>  	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
>  	select VIRT_CPU_ACCOUNTING
>  	select CONTEXT_TRACKING

> @@ -100,7 +100,6 @@ config NO_HZ_FULL
>  	# RCU_USER_QS dependency
>  	depends on HAVE_CONTEXT_TRACKING
>  	# VIRT_CPU_ACCOUNTING_GEN dependency
> -	depends on 64BIT
>  	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN

Yay!

Thanks,

	Ingo

[PATCH 1/3] vtime: Add HAVE_VIRT_CPU_ACCOUNTING_GEN Kconfig

[Frederic Weisbecker]

From: Kevin Hilman <khilman@linaro.org>

With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit. In order
to use that feature, arch code should be audited to ensure there are no
races in concurrent read/write of cputime_t. For example,
reading/writing 64-bit cputime_t on some 32-bit arches may require
multiple accesses for low and high value parts, so proper locking
is needed to protect against concurrent accesses.

Therefore, add CONFIG_HAVE_VIRT_CPU_ACCOUNTING_GEN which arches can
enable after they've been audited for potential races.

This option is automatically enabled on 64-bit platforms.

Feature requested by Frederic Weisbecker.

Signed-off-by: Kevin Hilman <khilman@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Arm Linux <linux-arm-kernel@lists.infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 arch/Kconfig        | 12 ++++++++++++
 init/Kconfig        |  1 +
 kernel/time/Kconfig |  1 +
 3 files changed, 14 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index af2cc6e..185f8b0 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -353,6 +353,18 @@ config HAVE_CONTEXT_TRACKING
 config HAVE_VIRT_CPU_ACCOUNTING
 	bool
 
+config HAVE_VIRT_CPU_ACCOUNTING_GEN
+	bool
+	default y if 64BIT
+	help
+	  With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
+	  Before enabling this option, arch code must be audited
+	  to ensure there are no races in concurrent read/write of
+	  cputime_t. For example, reading/writing 64-bit cputime_t on
+	  some 32-bit arches may require multiple accesses, so proper
+	  locking is needed to protect against concurrent accesses.
+
+
 config HAVE_IRQ_TIME_ACCOUNTING
 	bool
 	help
diff --git a/init/Kconfig b/init/Kconfig
index 3ecd8a1..68c1a0e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -355,6 +355,7 @@ config VIRT_CPU_ACCOUNTING_NATIVE
 config VIRT_CPU_ACCOUNTING_GEN
 	bool "Full dynticks CPU time accounting"
 	depends on HAVE_CONTEXT_TRACKING && 64BIT
+	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select VIRT_CPU_ACCOUNTING
 	select CONTEXT_TRACKING
 	help
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 2b62fe8..f148475 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -101,6 +101,7 @@ config NO_HZ_FULL
 	depends on HAVE_CONTEXT_TRACKING
 	# VIRT_CPU_ACCOUNTING_GEN dependency
 	depends on 64BIT
+	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select NO_HZ_COMMON
 	select RCU_USER_QS
 	select RCU_NOCB_CPU
-- 
1.8.3.1