diff mbox series

[PATCHv2,2/2] perf/core: Allow reading package events from perf_event_read_local

Message ID 20230913125956.3652667-1-tero.kristo@linux.intel.com
State New
Headers
Series None |

Commit Message

Tero Kristo Sept. 13, 2023, 12:59 p.m. UTC 
  Per-package perf events are typically registered with a single CPU only,
however they can be read across all the CPUs within the package.
Currently perf_event_read maps the event CPU according to the topology
information to avoid an unnecessary SMP call, however
perf_event_read_local deals with hard values and rejects a read with a
failure if the CPU is not the one exactly registered. Allow similar
mapping within the perf_event_read_local if the perf event in question
can support this.

This allows users like BPF code to read the package perf events properly
across different CPUs within a package.

Signed-off-by: Tero Kristo <tero.kristo@linux.intel.com>
---
v2:
  * prevent illegal array access in case event->oncpu == -1
  * split the event->cpu / event->oncpu handling to their own variables

 kernel/events/core.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

Comments

Peter Zijlstra Oct. 3, 2023, 11 a.m. UTC | #1 
On Wed, Sep 13, 2023 at 03:59:56PM +0300, Tero Kristo wrote:
> Per-package perf events are typically registered with a single CPU only,
> however they can be read across all the CPUs within the package.
> Currently perf_event_read maps the event CPU according to the topology
> information to avoid an unnecessary SMP call, however
> perf_event_read_local deals with hard values and rejects a read with a
> failure if the CPU is not the one exactly registered. Allow similar
> mapping within the perf_event_read_local if the perf event in question
> can support this.
> 
> This allows users like BPF code to read the package perf events properly
> across different CPUs within a package.
> 
> Signed-off-by: Tero Kristo <tero.kristo@linux.intel.com>
> ---
> v2:
>   * prevent illegal array access in case event->oncpu == -1
>   * split the event->cpu / event->oncpu handling to their own variables
> 
>  kernel/events/core.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4c72a41f11af..6b343bac0a71 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4425,6 +4425,9 @@ static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)
>  {
>  	u16 local_pkg, event_pkg;
>  
> +	if (event_cpu < 0 || event_cpu >= nr_cpu_ids)
> +		return event_cpu;

	if ((unsigned)event_cpu >= nr_cpu_ids)
		return event_cpu;

As you could also find at the current __perf_event_read_cpu() callsite.

> +
>  	if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
>  		int local_cpu = smp_processor_id();
>  
> @@ -4528,6 +4531,8 @@ int perf_event_read_local(struct perf_event *event, u64 *value,
>  {
>  	unsigned long flags;
>  	int ret = 0;
> +	int event_cpu;
> +	int event_oncpu;

You wrecked the x-mas tree :-)

I'll fix both up.

Thanks!
diff mbox series

Patch

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4c72a41f11af..6b343bac0a71 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4425,6 +4425,9 @@  static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)
 {
 	u16 local_pkg, event_pkg;
 
+	if (event_cpu < 0 || event_cpu >= nr_cpu_ids)
+		return event_cpu;
+
 	if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
 		int local_cpu = smp_processor_id();
 
@@ -4528,6 +4531,8 @@  int perf_event_read_local(struct perf_event *event, u64 *value,
 {
 	unsigned long flags;
 	int ret = 0;
+	int event_cpu;
+	int event_oncpu;
 
 	/*
 	 * Disabling interrupts avoids all counter scheduling (context
@@ -4551,15 +4556,22 @@  int perf_event_read_local(struct perf_event *event, u64 *value,
 		goto out;
 	}
 
+	/*
+	 * Get the event CPU numbers, and adjust them to local if the event is
+	 * a per-package event that can be read locally
+	 */
+	event_oncpu = __perf_event_read_cpu(event, event->oncpu);
+	event_cpu = __perf_event_read_cpu(event, event->cpu);
+
 	/* If this is a per-CPU event, it must be for this CPU */
 	if (!(event->attach_state & PERF_ATTACH_TASK) &&
-	    event->cpu != smp_processor_id()) {
+	    event_cpu != smp_processor_id()) {
 		ret = -EINVAL;
 		goto out;
 	}
 
 	/* If this is a pinned event it must be running on this CPU */
-	if (event->attr.pinned && event->oncpu != smp_processor_id()) {
+	if (event->attr.pinned && event_oncpu != smp_processor_id()) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -4569,7 +4581,7 @@  int perf_event_read_local(struct perf_event *event, u64 *value,
 	 * or local to this CPU. Furthermore it means its ACTIVE (otherwise
 	 * oncpu == -1).
 	 */
-	if (event->oncpu == smp_processor_id())
+	if (event_oncpu == smp_processor_id())
 		event->pmu->read(event);
 
 	*value = local64_read(&event->count);