[PATCH v5] arm64: Enable perf events based hard lockup detector

Subsystems: arm pmu profiling and debugging, arm64 port (aarch64 architecture), performance events subsystem, the rest

STALE1944d

9 messages, 3 authors, 2021-04-19 · open the first message on its own page

[PATCH v5] arm64: Enable perf events based hard lockup detector

From: Sumit Garg <hidden>
Date: 2021-01-15 12:02:54

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

Changes in v5:
- Fix lockup_detector_init() invocation to be rather invoked from CPU
  binded context as it makes heavy use of per-cpu variables and shouldn't
  be invoked from preemptible context.

Changes in v4:
- Rebased to latest pmu v7 NMI patch-set [1] and in turn use "has_nmi"
  hook to know if PMU IRQ has been requested as an NMI.
- Add check for return value prior to initializing hard-lockup detector.

[1] https://lkml.org/lkml/2020/9/24/458

Changes in v3:
- Rebased to latest pmu NMI patch-set [1].
- Addressed misc. comments from Stephen.

[1] https://lkml.org/lkml/2020/8/19/671

Changes since RFC:
- Rebased on top of Alex's WIP-pmu-nmi branch.
- Add comment for safe max. CPU frequency.
- Misc. cleanup.

 arch/arm64/Kconfig             |  2 ++
 arch/arm64/kernel/perf_event.c | 48 ++++++++++++++++++++++++++++++++++++++++--
 drivers/perf/arm_pmu.c         |  5 +++++
 include/linux/perf/arm_pmu.h   |  2 ++
 4 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f39568b..05e1735 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -174,6 +174,8 @@ config ARM64
 	select HAVE_NMI
 	select HAVE_PATA_PLATFORM
 	select HAVE_PERF_EVENTS
+	select HAVE_PERF_EVENTS_NMI if ARM64_PSEUDO_NMI && HW_PERF_EVENTS
+	select HAVE_HARDLOCKUP_DETECTOR_PERF if PERF_EVENTS && HAVE_PERF_EVENTS_NMI
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 3605f77a..bafb7c8 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c

@@ -23,6 +23,8 @@
 #include <linux/platform_device.h>
 #include <linux/sched_clock.h>
 #include <linux/smp.h>
+#include <linux/nmi.h>
+#include <linux/cpufreq.h>
 
 /* ARMv8 Cortex-A53 specific event types. */
 #define ARMV8_A53_PERFCTR_PREF_LINEFILL				0xC2

@@ -1246,12 +1248,30 @@ static struct platform_driver armv8_pmu_driver = {
 	.probe		= armv8_pmu_device_probe,
 };
 
+static int __init lockup_detector_init_fn(void *data)
+{
+	lockup_detector_init();
+	return 0;
+}
+
 static int __init armv8_pmu_driver_init(void)
 {
+	int ret;
+
 	if (acpi_disabled)
-		return platform_driver_register(&armv8_pmu_driver);
+		ret = platform_driver_register(&armv8_pmu_driver);
 	else
-		return arm_pmu_acpi_probe(armv8_pmuv3_init);
+		ret = arm_pmu_acpi_probe(armv8_pmuv3_init);
+
+	/*
+	 * Try to re-initialize lockup detector after PMU init in
+	 * case PMU events are triggered via NMIs.
+	 */
+	if (ret == 0 && arm_pmu_irq_is_nmi())
+		smp_call_on_cpu(raw_smp_processor_id(), lockup_detector_init_fn,
+				NULL, false);
+
+	return ret;
 }
 device_initcall(armv8_pmu_driver_init)

@@ -1309,3 +1329,27 @@ void arch_perf_update_userpage(struct perf_event *event,
 	userpg->cap_user_time_zero = 1;
 	userpg->cap_user_time_short = 1;
 }
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR_PERF
+/*
+ * Safe maximum CPU frequency in case a particular platform doesn't implement
+ * cpufreq driver. Although, architecture doesn't put any restrictions on
+ * maximum frequency but 5 GHz seems to be safe maximum given the available
+ * Arm CPUs in the market which are clocked much less than 5 GHz. On the other
+ * hand, we can't make it much higher as it would lead to a large hard-lockup
+ * detection timeout on parts which are running slower (eg. 1GHz on
+ * Developerbox) and doesn't possess a cpufreq driver.
+ */
+#define SAFE_MAX_CPU_FREQ	5000000000UL // 5 GHz
+u64 hw_nmi_get_sample_period(int watchdog_thresh)
+{
+	unsigned int cpu = smp_processor_id();
+	unsigned long max_cpu_freq;
+
+	max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
+	if (!max_cpu_freq)
+		max_cpu_freq = SAFE_MAX_CPU_FREQ;
+
+	return (u64)max_cpu_freq * watchdog_thresh;
+}
+#endif

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index cb2f55f..794a37d 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c

@@ -726,6 +726,11 @@ static int armpmu_get_cpu_irq(struct arm_pmu *pmu, int cpu)
 	return per_cpu(hw_events->irq, cpu);
 }
 
+bool arm_pmu_irq_is_nmi(void)
+{
+	return has_nmi;
+}
+
 /*
  * PMU hardware loses all context when a CPU goes offline.
  * When a CPU is hotplugged back in, since some hardware registers are

diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 5054802..bf79667 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h

@@ -163,6 +163,8 @@ int arm_pmu_acpi_probe(armpmu_init_fn init_fn);
 static inline int arm_pmu_acpi_probe(armpmu_init_fn init_fn) { return 0; }
 #endif
 
+bool arm_pmu_irq_is_nmi(void);
+
 /* Internal functions only for core arm_pmu code */
 struct arm_pmu *armpmu_alloc(void);
 struct arm_pmu *armpmu_alloc_atomic(void);

-- 
2.7.4


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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Will Deacon <will@kernel.org>
Date: 2021-01-26 14:20:11

Hi Sumit,

On Fri, Jan 15, 2021 at 05:31:41PM +0530, Sumit Garg wrote:

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

[...]

quoted hunk

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 3605f77a..bafb7c8 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c

@@ -23,6 +23,8 @@
 #include <linux/platform_device.h>
 #include <linux/sched_clock.h>
 #include <linux/smp.h>
+#include <linux/nmi.h>
+#include <linux/cpufreq.h>
 
 /* ARMv8 Cortex-A53 specific event types. */
 #define ARMV8_A53_PERFCTR_PREF_LINEFILL				0xC2

@@ -1246,12 +1248,30 @@ static struct platform_driver armv8_pmu_driver = {
 	.probe		= armv8_pmu_device_probe,
 };
 
+static int __init lockup_detector_init_fn(void *data)
+{
+	lockup_detector_init();
+	return 0;
+}
+
 static int __init armv8_pmu_driver_init(void)
 {
+	int ret;
+
 	if (acpi_disabled)
-		return platform_driver_register(&armv8_pmu_driver);
+		ret = platform_driver_register(&armv8_pmu_driver);
 	else
-		return arm_pmu_acpi_probe(armv8_pmuv3_init);
+		ret = arm_pmu_acpi_probe(armv8_pmuv3_init);
+
+	/*
+	 * Try to re-initialize lockup detector after PMU init in
+	 * case PMU events are triggered via NMIs.
+	 */
+	if (ret == 0 && arm_pmu_irq_is_nmi())
+		smp_call_on_cpu(raw_smp_processor_id(), lockup_detector_init_fn,
+				NULL, false);
+
+	return ret;

What's wrong with the alternative approach outlined by Mark:

https://lore.kernel.org/r/20210113130235.GB19011@C02TD0UTHF1T.local

?

Will

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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Sumit Garg <hidden>
Date: 2021-01-28 07:09:43

Hi Will,

On Tue, 26 Jan 2021 at 19:48, Will Deacon [off-list ref] wrote:

Hi Sumit,

On Fri, Jan 15, 2021 at 05:31:41PM +0530, Sumit Garg wrote:

quoted

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

[...]

quoted

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 3605f77a..bafb7c8 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c

@@ -23,6 +23,8 @@
 #include <linux/platform_device.h>
 #include <linux/sched_clock.h>
 #include <linux/smp.h>
+#include <linux/nmi.h>
+#include <linux/cpufreq.h>

 /* ARMv8 Cortex-A53 specific event types. */
 #define ARMV8_A53_PERFCTR_PREF_LINEFILL                              0xC2

@@ -1246,12 +1248,30 @@ static struct platform_driver armv8_pmu_driver = {
      .probe          = armv8_pmu_device_probe,
 };

+static int __init lockup_detector_init_fn(void *data)
+{
+     lockup_detector_init();
+     return 0;
+}
+
 static int __init armv8_pmu_driver_init(void)
 {
+     int ret;
+
      if (acpi_disabled)
-             return platform_driver_register(&armv8_pmu_driver);
+             ret = platform_driver_register(&armv8_pmu_driver);
      else
-             return arm_pmu_acpi_probe(armv8_pmuv3_init);
+             ret = arm_pmu_acpi_probe(armv8_pmuv3_init);
+
+     /*
+      * Try to re-initialize lockup detector after PMU init in
+      * case PMU events are triggered via NMIs.
+      */
+     if (ret == 0 && arm_pmu_irq_is_nmi())
+             smp_call_on_cpu(raw_smp_processor_id(), lockup_detector_init_fn,
+                             NULL, false);
+
+     return ret;

What's wrong with the alternative approach outlined by Mark:

https://lore.kernel.org/r/20210113130235.GB19011@C02TD0UTHF1T.local

?

I have replied on this thread.

-Sumit

Will

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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Sumit Garg <hidden>
Date: 2021-02-19 09:38:59

Hi Will, Mark,

On Fri, 15 Jan 2021 at 17:32, Sumit Garg [off-list ref] wrote:

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

Changes in v5:
- Fix lockup_detector_init() invocation to be rather invoked from CPU
  binded context as it makes heavy use of per-cpu variables and shouldn't
  be invoked from preemptible context.

Do you have any further comments on this?

Lecopzer,

Does this feature work fine for you now?

-Sumit

quoted hunk

Changes in v4:
- Rebased to latest pmu v7 NMI patch-set [1] and in turn use "has_nmi"
  hook to know if PMU IRQ has been requested as an NMI.
- Add check for return value prior to initializing hard-lockup detector.

[1] https://lkml.org/lkml/2020/9/24/458

Changes in v3:
- Rebased to latest pmu NMI patch-set [1].
- Addressed misc. comments from Stephen.

[1] https://lkml.org/lkml/2020/8/19/671

Changes since RFC:
- Rebased on top of Alex's WIP-pmu-nmi branch.
- Add comment for safe max. CPU frequency.
- Misc. cleanup.

 arch/arm64/Kconfig             |  2 ++
 arch/arm64/kernel/perf_event.c | 48 ++++++++++++++++++++++++++++++++++++++++--
 drivers/perf/arm_pmu.c         |  5 +++++
 include/linux/perf/arm_pmu.h   |  2 ++
 4 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f39568b..05e1735 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -174,6 +174,8 @@ config ARM64
        select HAVE_NMI
        select HAVE_PATA_PLATFORM
        select HAVE_PERF_EVENTS
+       select HAVE_PERF_EVENTS_NMI if ARM64_PSEUDO_NMI && HW_PERF_EVENTS
+       select HAVE_HARDLOCKUP_DETECTOR_PERF if PERF_EVENTS && HAVE_PERF_EVENTS_NMI
        select HAVE_PERF_REGS
        select HAVE_PERF_USER_STACK_DUMP
        select HAVE_REGS_AND_STACK_ACCESS_API

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 3605f77a..bafb7c8 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c

@@ -23,6 +23,8 @@
 #include <linux/platform_device.h>
 #include <linux/sched_clock.h>
 #include <linux/smp.h>
+#include <linux/nmi.h>
+#include <linux/cpufreq.h>

 /* ARMv8 Cortex-A53 specific event types. */
 #define ARMV8_A53_PERFCTR_PREF_LINEFILL                                0xC2

@@ -1246,12 +1248,30 @@ static struct platform_driver armv8_pmu_driver = {
        .probe          = armv8_pmu_device_probe,
 };

+static int __init lockup_detector_init_fn(void *data)
+{
+       lockup_detector_init();
+       return 0;
+}
+
 static int __init armv8_pmu_driver_init(void)
 {
+       int ret;
+
        if (acpi_disabled)
-               return platform_driver_register(&armv8_pmu_driver);
+               ret = platform_driver_register(&armv8_pmu_driver);
        else
-               return arm_pmu_acpi_probe(armv8_pmuv3_init);
+               ret = arm_pmu_acpi_probe(armv8_pmuv3_init);
+
+       /*
+        * Try to re-initialize lockup detector after PMU init in
+        * case PMU events are triggered via NMIs.
+        */
+       if (ret == 0 && arm_pmu_irq_is_nmi())
+               smp_call_on_cpu(raw_smp_processor_id(), lockup_detector_init_fn,
+                               NULL, false);
+
+       return ret;
 }
 device_initcall(armv8_pmu_driver_init)

@@ -1309,3 +1329,27 @@ void arch_perf_update_userpage(struct perf_event *event,
        userpg->cap_user_time_zero = 1;
        userpg->cap_user_time_short = 1;
 }
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR_PERF
+/*
+ * Safe maximum CPU frequency in case a particular platform doesn't implement
+ * cpufreq driver. Although, architecture doesn't put any restrictions on
+ * maximum frequency but 5 GHz seems to be safe maximum given the available
+ * Arm CPUs in the market which are clocked much less than 5 GHz. On the other
+ * hand, we can't make it much higher as it would lead to a large hard-lockup
+ * detection timeout on parts which are running slower (eg. 1GHz on
+ * Developerbox) and doesn't possess a cpufreq driver.
+ */
+#define SAFE_MAX_CPU_FREQ      5000000000UL // 5 GHz
+u64 hw_nmi_get_sample_period(int watchdog_thresh)
+{
+       unsigned int cpu = smp_processor_id();
+       unsigned long max_cpu_freq;
+
+       max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
+       if (!max_cpu_freq)
+               max_cpu_freq = SAFE_MAX_CPU_FREQ;
+
+       return (u64)max_cpu_freq * watchdog_thresh;
+}
+#endif

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index cb2f55f..794a37d 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c

@@ -726,6 +726,11 @@ static int armpmu_get_cpu_irq(struct arm_pmu *pmu, int cpu)
        return per_cpu(hw_events->irq, cpu);
 }

+bool arm_pmu_irq_is_nmi(void)
+{
+       return has_nmi;
+}
+
 /*
  * PMU hardware loses all context when a CPU goes offline.
  * When a CPU is hotplugged back in, since some hardware registers are

diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 5054802..bf79667 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h

@@ -163,6 +163,8 @@ int arm_pmu_acpi_probe(armpmu_init_fn init_fn);
 static inline int arm_pmu_acpi_probe(armpmu_init_fn init_fn) { return 0; }
 #endif

+bool arm_pmu_irq_is_nmi(void);
+
 /* Internal functions only for core arm_pmu code */
 struct arm_pmu *armpmu_alloc(void);
 struct arm_pmu *armpmu_alloc_atomic(void);
--

2.7.4

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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Lecopzer Chen <hidden>
Date: 2021-03-30 08:07:06

Hi Will, Mark,

On Fri, 15 Jan 2021 at 17:32, Sumit Garg [off-list ref] wrote:

quoted

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

Changes in v5:
- Fix lockup_detector_init() invocation to be rather invoked from CPU
  binded context as it makes heavy use of per-cpu variables and shouldn't
  be invoked from preemptible context.

Do you have any further comments on this?

Lecopzer,

Does this feature work fine for you now?

This really fixes the warning, I have a real hardware for testing this now.
but do we need to call lockup_detector_init() for each cpu?

In init/main.c, it's only called by cpu 0 for once.


BRs,
Lecopzer
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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Lecopzer Chen <hidden>
Date: 2021-03-30 08:33:05

quoted

Hi Will, Mark,

On Fri, 15 Jan 2021 at 17:32, Sumit Garg [off-list ref] wrote:

quoted

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

Changes in v5:
- Fix lockup_detector_init() invocation to be rather invoked from CPU
  binded context as it makes heavy use of per-cpu variables and shouldn't
  be invoked from preemptible context.

Do you have any further comments on this?

Lecopzer,

Does this feature work fine for you now?

This really fixes the warning, I have a real hardware for testing this now.
but do we need to call lockup_detector_init() for each cpu?

In init/main.c, it's only called by cpu 0 for once.

 
Oh sorry, I just misread the code, please ignore previous mail.
 

BRs,
Lecopzer
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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Sumit Garg <hidden>
Date: 2021-03-30 12:31:44

On Tue, 30 Mar 2021 at 14:07, Lecopzer Chen [off-list ref] wrote:

quoted

Hi Will, Mark,

On Fri, 15 Jan 2021 at 17:32, Sumit Garg [off-list ref] wrote:

quoted

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

Changes in v5:
- Fix lockup_detector_init() invocation to be rather invoked from CPU
  binded context as it makes heavy use of per-cpu variables and shouldn't
  be invoked from preemptible context.

Do you have any further comments on this?

Lecopzer,

Does this feature work fine for you now?

This really fixes the warning, I have a real hardware for testing this now.

Thanks for the testing. I assume it as an implicit Tested-by.

quoted

but do we need to call lockup_detector_init() for each cpu?

In init/main.c, it's only called by cpu 0 for once.

Oh sorry, I just misread the code, please ignore previous mail.

No worries.

-Sumit

BRs,
Lecopzer

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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Sumit Garg <hidden>
Date: 2021-04-12 12:01:31

Hi Will,

On Tue, 30 Mar 2021 at 18:00, Sumit Garg [off-list ref] wrote:

On Tue, 30 Mar 2021 at 14:07, Lecopzer Chen [off-list ref] wrote:

quoted

Hi Will, Mark,

On Fri, 15 Jan 2021 at 17:32, Sumit Garg [off-list ref] wrote:

quoted

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

Changes in v5:
- Fix lockup_detector_init() invocation to be rather invoked from CPU
  binded context as it makes heavy use of per-cpu variables and shouldn't
  be invoked from preemptible context.

Do you have any further comments on this?

Since there aren't any further comments, can you re-pick this feature for 5.13?

-Sumit

quoted

Lecopzer,

Does this feature work fine for you now?

This really fixes the warning, I have a real hardware for testing this now.

Thanks for the testing. I assume it as an implicit Tested-by.

quoted

but do we need to call lockup_detector_init() for each cpu?

In init/main.c, it's only called by cpu 0 for once.

Oh sorry, I just misread the code, please ignore previous mail.

No worries.

-Sumit

quoted

BRs,
Lecopzer

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Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

From: Will Deacon <will@kernel.org>
Date: 2021-04-19 17:03:43

On Mon, Apr 12, 2021 at 05:31:13PM +0530, Sumit Garg wrote:

On Tue, 30 Mar 2021 at 18:00, Sumit Garg [off-list ref] wrote:

quoted

On Tue, 30 Mar 2021 at 14:07, Lecopzer Chen [off-list ref] wrote:

quoted

On Fri, 15 Jan 2021 at 17:32, Sumit Garg [off-list ref] wrote:

quoted

With the recent feature added to enable perf events to use pseudo NMIs
as interrupts on platforms which support GICv3 or later, its now been
possible to enable hard lockup detector (or NMI watchdog) on arm64
platforms. So enable corresponding support.

One thing to note here is that normally lockup detector is initialized
just after the early initcalls but PMU on arm64 comes up much later as
device_initcall(). So we need to re-initialize lockup detection once
PMU has been initialized.

Signed-off-by: Sumit Garg <redacted>
---

Changes in v5:
- Fix lockup_detector_init() invocation to be rather invoked from CPU
  binded context as it makes heavy use of per-cpu variables and shouldn't
  be invoked from preemptible context.

Do you have any further comments on this?

Since there aren't any further comments, can you re-pick this feature for 5.13?

I'd still like Mark's Ack on this, as the approach you have taken doesn't
really sit with what he was suggesting.

I also don't understand how all the CPUs get initialised with your patch,
since the PMU driver will be initialised after SMP is up and running.

Will

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