[RFC PATCH 08/15] ARM: perf: remove unnecessary armpmu->stop

[RFC PATCH 08/15] ARM: perf: remove unnecessary armpmu->stop

[Mark Rutland]

As armpmu_disable will call armpmu->stop when the last event has been
removed, this is pointless and simply adds to the noise when debugging.
Additionally, due to this call occurring in a preemptible context, this
is problematic for per-cpu locking of PMU registers (where we will
attempt to access per-cpu spinlock for use with raw_spin_lock_irqsave).

This patch removes the call to armpmu->stop.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/kernel/perf_event.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 9d6ac99..5ce6c33 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -396,7 +396,6 @@ armpmu_release_hardware(void)
 			free_irq(irq, NULL);
 	}
 
-	armpmu->stop();
 	release_pmu(ARM_PMU_DEVICE_CPU);
 }
 
-- 
1.7.0.4

[RFC PATCH 00/15] ARM: perf: support multiple PMUs

[Mark Rutland]

System (AKA nest or uncore) PMUs exist on devices which are not affine
to a single CPU. They usually cannot be directly associated with
individual tasks and are asynchronous with respect to the current
execution. Examples of devices which could have system PMUs include L2
cache controllers, GPUs and memory buses.

The following patch series refactors the ARM PMU backend, enabling
new PMUs to reuse the existing code. This should allow for system PMUs
to be supported in future. Further work will be required to get perf to
fully understand system PMUs, but this provides something usable.

The framework is intended to be used by system PMUs which hang off core
platform components (e.g. L2 cache, AXI bus). If a device is complex
enough or separate enough from core functionality to have its own
driver, it should implement its own PMU handling using the core perf
API directly.

The first patch ("perf: provide PMU when initing events") is currently
sitting in the tip tree, but as it's required for event initialization
to function (and hence for the PMU to be usable), it's provided here
for convenience.

The series is based on Will Deacon's perf-updates branch at:
	git://linux-arm.org/linux-2.6-wd.git perf-updates

An example driver using the framework (supporting the PMU present in
L220/PL310 level 2 cache controllers) can be found at:
	git://linux-arm.org/linux-2.6-wd.git perf-l2x0-wip

Any comments would be welcome.

Thanks,
Mark.

Mark Rutland (15):
  perf: provide PMU when initing events
  ARM: perf: only register a CPU PMU when present
  ARM: perf: clean up event group validation
  ARM: perf: remove active_mask
  ARM: perf: move active_events into struct arm_pmu
  ARM: perf: move platform device to struct arm_pmu
  ARM: perf: indirect access to cpu_hw_events
  ARM: perf: remove unnecessary armpmu->stop
  ARM: perf: lock PMU registers per-CPU
  ARM: perf: add type field to struct arm_pmu
  ARM: perf: refactor event mapping
  ARM: perf: add support for multiple PMUs
  ARM: perf: remove event limit from pmu_hw_events
  ARM: perf: remove cpu-related misnomers
  ARM: perf: move arm_pmu into <asm/pmu.h>

 arch/arm/include/asm/pmu.h          |   64 +++++++
 arch/arm/kernel/perf_event.c        |  318 +++++++++++++++++------------------
 arch/arm/kernel/perf_event_v6.c     |   73 ++++++---
 arch/arm/kernel/perf_event_v7.c     |   74 +++++---
 arch/arm/kernel/perf_event_xscale.c |   76 +++++----
 kernel/events/core.c                |    4 +-
 6 files changed, 359 insertions(+), 250 deletions(-)

[RFC PATCH 08/15] ARM: perf: remove unnecessary armpmu->stop

[Mark Rutland]

As armpmu_disable will call armpmu->stop when the last event has been
removed, this is pointless and simply adds to the noise when debugging.
Additionally, due to this call occurring in a preemptible context, this
is problematic for per-cpu locking of PMU registers (where we will
attempt to access per-cpu spinlock for use with raw_spin_lock_irqsave).

This patch removes the call to armpmu->stop.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/kernel/perf_event.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 9d6ac99..5ce6c33 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -396,7 +396,6 @@ armpmu_release_hardware(void)
 			free_irq(irq, NULL);
 	}
 
-	armpmu->stop();
 	release_pmu(ARM_PMU_DEVICE_CPU);
 }
 
-- 
1.7.0.4

[RFC PATCH 08/15] ARM: perf: remove unnecessary armpmu->stop

[Ashwin Chaugule]

Hello,

>> From: Mark Rutland 
>>
>> As armpmu_disable will call armpmu->stop when the last event has been
>> removed, this is pointless and simply adds to the noise when debugging.
>> Additionally, due to this call occurring in a preemptible context, this
>> is problematic for per-cpu locking of PMU registers (where we will
>> attempt to access per-cpu spinlock for use with raw_spin_lock_irqsave).
>>
>> This patch removes the call to armpmu->stop.
>>
>> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
>> Reviewed-by: Will Deacon <will.deacon@arm.com>
>> ---
>> arch/arm/kernel/perf_event.c |    1 -
>> 1 files changed, 0 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
>> index 9d6ac99..5ce6c33 100644
>> --- a/arch/arm/kernel/perf_event.c
>> +++ b/arch/arm/kernel/perf_event.c
>> @@ -396,7 +396,6 @@ armpmu_release_hardware(void)
>> 			free_irq(irq, NULL);
>> 	}
>>
>> -	armpmu->stop();
>> 	release_pmu(ARM_PMU_DEVICE_CPU);


Makes sense. On a similar note, I've been wondering why we need to loop
through all events in armpmu_enable() ?

Wouldn't the event->add call have taken care of armpmu->enable prior to
calling armpmu_enable() ?

I think we just need an armpmu->start(). What are your thoughts ?

Cheers,
Ashwin

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

[RFC PATCH 08/15] ARM: perf: remove unnecessary armpmu->stop

[Will Deacon]

On Mon, Aug 22, 2011 at 07:36:18PM +0100, Ashwin Chaugule wrote:
> Hello,

Hi Ashwin,

> >> From: Mark Rutland 
> >>
> >> As armpmu_disable will call armpmu->stop when the last event has been
> >> removed, this is pointless and simply adds to the noise when debugging.
> >> Additionally, due to this call occurring in a preemptible context, this
> >> is problematic for per-cpu locking of PMU registers (where we will
> >> attempt to access per-cpu spinlock for use with raw_spin_lock_irqsave).
> >>
> >> This patch removes the call to armpmu->stop.
> >>
> >> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> >> Reviewed-by: Will Deacon <will.deacon@arm.com>
> >> ---
> >> arch/arm/kernel/perf_event.c |    1 -
> >> 1 files changed, 0 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
> >> index 9d6ac99..5ce6c33 100644
> >> --- a/arch/arm/kernel/perf_event.c
> >> +++ b/arch/arm/kernel/perf_event.c
> >> @@ -396,7 +396,6 @@ armpmu_release_hardware(void)
> >> 			free_irq(irq, NULL);
> >> 	}
> >>
> >> -	armpmu->stop();
> >> 	release_pmu(ARM_PMU_DEVICE_CPU);
> 
> 
> Makes sense. On a similar note, I've been wondering why we need to loop
> through all events in armpmu_enable() ?
> 
> Wouldn't the event->add call have taken care of armpmu->enable prior to
> calling armpmu_enable() ?

Hmm, I think you might be right. armpmu->enable is called from armpmu_start,
which is called from armpmu->add whenever a new event is added. The current
redundancy is likely a hangover from before we had the PERF_EF_*/PERF_HES_*
flags.

> I think we just need an armpmu->start(). What are your thoughts ?

Yes, conditional on armpmu->num_events > 0. I'll give it a spin and add it to
my perf-updates branch if I don't see any regressions.

Cheers,

Will