On Wed, Aug 13, 2025 at 06:01:10PM +0100, Robin Murphy wrote:
> 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.mur...@arm.com>
To bikeshed a little here, I'm not keen on the PERF_PMU_CAP_RAW_EVENTS
name, because it's not clear what "RAW" really means, and people will
definitely read that to mean something else.
Could we go with something like PERF_PMU_CAP_COMMON_CPU_EVENTS, to make
it clear that this is about opting into CPU-PMU specific event types (of
which PERF_TYPE_RAW is one of)?
Likewise, s/is_raw_pmu()/pmu_supports_common_cpu_events()/.
> ---
>
> 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...
I reckon we don't need to automagically do that, but I reckon that
is_raw_pmu()/pmu_supports_common_cpu_events() should only check the cap,
and we don't read anything special into any of
PERF_TYPE_{RAW,HARDWARE,HW_CACHE}.
> ---
> 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,
Tangential, but use of perf_sw_context here looks bogus.
> 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;
> +}
As above, I reckon we should make this:
static bool pmu_supports_common_cpu_events(const struct pmu *pmu)
{
return pmu->capabilities & PERF_PMU_CAP_RAW_EVENTS;
}
Other than the above, this looks good to me.
Mark.
> +
> 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)))
> + return -ENOENT;
> +
> if (!try_module_get(pmu->module))
> return -ENODEV;
>
> --
> 2.39.2.101.g768bb238c484.dirty
>
