Re: [PATCH 18/19] perf: Introduce positive capability for raw events

On 8/19/25 15:15, Robin Murphy wrote:

On 13/08/2025 6:01 pm, Robin Murphy wrote:

quoted

Only a handful of CPU PMUs accept PERF_TYPE_{RAW,HARDWARE,HW_CACHE}
events without registering themselves as PERF_TYPE_RAW in the first
place. Add an explicit opt-in for these special cases, so that we can
make life easier for every other driver (and probably also speed up the
slow-path search) by having perf_try_init_event() do the basic type
checking to cover the majority of cases.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

A further possibility is to automatically add the cap to PERF_TYPE_RAW
PMUs in perf_pmu_register() to have a single point-of-use condition; I'm
undecided...
---
  arch/s390/kernel/perf_cpum_cf.c    |  1 +
  arch/s390/kernel/perf_pai_crypto.c |  2 +-
  arch/s390/kernel/perf_pai_ext.c    |  2 +-
  arch/x86/events/core.c             |  2 +-
  drivers/perf/arm_pmu.c             |  1 +
  include/linux/perf_event.h         |  1 +
  kernel/events/core.c               | 15 +++++++++++++++
  7 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
index 1a94e0944bc5..782ab755ddd4 100644
--- a/arch/s390/kernel/perf_cpum_cf.c
+++ b/arch/s390/kernel/perf_cpum_cf.c

@@ -1054,6 +1054,7 @@ static void cpumf_pmu_del(struct perf_event *event, int flags)

  /* Performance monitoring unit for s390x */
  static struct pmu cpumf_pmu = {
      .task_ctx_nr  = perf_sw_context,
+    .capabilities = PERF_PMU_CAP_RAW_EVENTS,
      .pmu_enable   = cpumf_pmu_enable,
      .pmu_disable  = cpumf_pmu_disable,
      .event_init   = cpumf_pmu_event_init,

diff --git a/arch/s390/kernel/perf_pai_crypto.c b/arch/s390/kernel/perf_pai_crypto.c
index a64b6b056a21..b5b6d8b5d943 100644
--- a/arch/s390/kernel/perf_pai_crypto.c
+++ b/arch/s390/kernel/perf_pai_crypto.c

@@ -569,7 +569,7 @@ static const struct attribute_group *paicrypt_attr_groups[] = {

  /* Performance monitoring unit for mapped counters */
  static struct pmu paicrypt = {
      .task_ctx_nr  = perf_hw_context,
-    .capabilities = PERF_PMU_CAP_SAMPLING,
+    .capabilities = PERF_PMU_CAP_SAMPLING | PERF_PMU_CAP_RAW_EVENTS,
      .event_init   = paicrypt_event_init,
      .add          = paicrypt_add,
      .del          = paicrypt_del,

diff --git a/arch/s390/kernel/perf_pai_ext.c b/arch/s390/kernel/perf_pai_ext.c
index 1261f80c6d52..bcd28c38da70 100644
--- a/arch/s390/kernel/perf_pai_ext.c
+++ b/arch/s390/kernel/perf_pai_ext.c

@@ -595,7 +595,7 @@ static const struct attribute_group *paiext_attr_groups[] = {

  /* Performance monitoring unit for mapped counters */
  static struct pmu paiext = {
      .task_ctx_nr  = perf_hw_context,
-    .capabilities = PERF_PMU_CAP_SAMPLING,
+    .capabilities = PERF_PMU_CAP_SAMPLING | PERF_PMU_CAP_RAW_EVENTS,
      .event_init   = paiext_event_init,
      .add          = paiext_add,
      .del          = paiext_del,

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 789dfca2fa67..764728bb80ae 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c

@@ -2697,7 +2697,7 @@ static bool x86_pmu_filter(struct pmu *pmu, int cpu)

  }
    static struct pmu pmu = {
-    .capabilities        = PERF_PMU_CAP_SAMPLING,
+    .capabilities        = PERF_PMU_CAP_SAMPLING | PERF_PMU_CAP_RAW_EVENTS,
        .pmu_enable        = x86_pmu_enable,
      .pmu_disable        = x86_pmu_disable,

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 72d8f38d0aa5..bc772a3bf411 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c

@@ -877,6 +877,7 @@ struct arm_pmu *armpmu_alloc(void)

           * specific PMU.
           */
          .capabilities    = PERF_PMU_CAP_SAMPLING |
+                  PERF_PMU_CAP_RAW_EVENTS |
                    PERF_PMU_CAP_EXTENDED_REGS |
                    PERF_PMU_CAP_EXTENDED_HW_TYPE,
      };

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 183b7c48b329..c6ad036c0037 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h

@@ -305,6 +305,7 @@ struct perf_event_pmu_context;

  #define PERF_PMU_CAP_EXTENDED_HW_TYPE    0x0100
  #define PERF_PMU_CAP_AUX_PAUSE        0x0200
  #define PERF_PMU_CAP_AUX_PREFER_LARGE    0x0400
+#define PERF_PMU_CAP_RAW_EVENTS        0x0800
    /**
   * pmu::scope

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 71b2a6730705..2ecee76d2ae2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c

@@ -12556,11 +12556,26 @@ static inline bool has_extended_regs(struct perf_event *event)

             (event->attr.sample_regs_intr & PERF_REG_EXTENDED_MASK);
  }
  +static bool is_raw_pmu(const struct pmu *pmu)
+{
+    return pmu->type == PERF_TYPE_RAW ||
+           pmu->capabilities & PERF_PMU_CAP_RAW_EVENTS;
+}
+
  static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
  {
      struct perf_event_context *ctx = NULL;
      int ret;
  +    /*
+     * Before touching anything, we can safely skip:
+     * - any event for a specific PMU which is not this one
+     * - any common event if this PMU doesn't support them
+     */
+    if (event->attr.type != pmu->type &&
+        (event->attr.type >= PERF_TYPE_MAX || is_raw_pmu(pmu)))

Ah, that should be "!is_raw_pmu(pmu)" there (although it's not entirely the cause of the LKP report on the final patch.)

Thanks,
Robin.

quoted

+        return -ENOENT;
+
      if (!try_module_get(pmu->module))
          return -ENODEV;
  

Hi Robin,

what is the intention of that patch?
Can you explain that a bit more.

Thanks.

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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