On 10/11/22 14:51, Anshuman Khandual wrote:

On 10/10/22 19:47, James Clark wrote:

quoted

On 06/10/2022 14:37, James Clark wrote:

quoted

On 29/09/2022 08:58, Anshuman Khandual wrote:

quoted

This adds arm pmu infrastrure to probe BRBE implementation's attributes via
driver exported callbacks later. The actual BRBE feature detection will be
added by the driver itself.

CPU specific BRBE entries, cycle count, format support gets detected during
PMU init. This information gets saved in per-cpu struct pmu_hw_events which
later helps in operating BRBE during a perf event context.

Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
 drivers/perf/arm_pmu_platform.c | 34 +++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/perf/arm_pmu_platform.c b/drivers/perf/arm_pmu_platform.c
index 933b96e243b8..acdc445081aa 100644
--- a/drivers/perf/arm_pmu_platform.c
+++ b/drivers/perf/arm_pmu_platform.c

@@ -172,6 +172,36 @@ static int armpmu_request_irqs(struct arm_pmu *armpmu)
 	return err;
 }
 
+static void arm_brbe_probe_cpu(void *info)
+{
+	struct pmu_hw_events *hw_events;
+	struct arm_pmu *armpmu = info;
+
+	/*
+	 * Return from here, if BRBE driver has not been
+	 * implemented for this PMU. This helps prevent
+	 * kernel crash later when brbe_probe() will be
+	 * called on the PMU.
+	 */
+	if (!armpmu->brbe_probe)
+		return;
+
+	hw_events = per_cpu_ptr(armpmu->hw_events, smp_processor_id());
+	armpmu->brbe_probe(hw_events);
+}
+
+static int armpmu_request_brbe(struct arm_pmu *armpmu)
+{
+	int cpu, err = 0;
+
+	for_each_cpu(cpu, &armpmu->supported_cpus) {
+		err = smp_call_function_single(cpu, arm_brbe_probe_cpu, armpmu, 1);

Hi Anshuman,

I have LOCKDEP on and the patchset applied to perf/core (82aad7ff7) on
git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git and I get

Can you confirm if this is currently the correct place to apply this to?

This series applied on v6.0-rc5 after the perf ABI changes, both in kernel
and in user space tools.

quoted

I'm only getting 0 length branch stacks now. Seems like it could be
something to do with the layout of perf samples because I know that was
done in separate commits:

Right, might be.

quoted

  sudo ./perf record -j any_call -- ls
  ./perf report -D | grep "branch stack"
  ... branch stack: nr:0
  ... branch stack: nr:0
  ... branch stack: nr:0
  ... branch stack: nr:0

I am planning to respin the series on 6.1-rc1 next week which should solve
these multiple moving parts problem

There are some recent changes which require PMU driver to set data.sample_flags
indicating what kind of records are being filled in there. Here are the commits

a9a931e2666878343 ("perf: Use sample_flags for branch stack")
3aac580d5cc3001ca ("perf: Add sample_flags to indicate the PMU-filled sample data")

Following fix solves the problem for BRBE driver.

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 98e9a615d3cb..85a3aaefc0fb 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c

@@ -877,6 +877,7 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
                if (has_branch_stack(event)) {
                        cpu_pmu->brbe_read(cpuc, event);
                        data.br_stack = &cpuc->branches->brbe_stack;
+                       data.sample_flags |= PERF_SAMPLE_BRANCH_STACK;
                        cpu_pmu->brbe_reset(cpuc);
                }
 

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