[PATCH v3 05/23] perf: Add a pmu capability for "exclusive" events

Alexander Shishkin
2014-08-11T05:27:08Z

Usually, pmus that do, for example, instruction tracing, would only ever
be able to have one event per task per cpu (or per perf_context). For such
pmus it makes sense to disallow creating conflicting events early on, so
as to provide consistent behavior for the user.

This patch adds a pmu capability that indicates such constraint on event
creation.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 46 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 71be27169c..b8902ebcb7 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -172,6 +172,7 @@ struct perf_event;
#define PERF_PMU_CAP_NO_INTERRUPT 0x01
#define PERF_PMU_CAP_AUX_NO_SG 0x02
#define PERF_PMU_CAP_AUX_SW_DOUBLEBUF 0x04
+#define PERF_PMU_CAP_EXCLUSIVE 0x08

/**
* struct pmu - generic performance monitoring unit
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c07768d0a0..361a45eee2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7149,6 +7149,32 @@ out:
return ret;
}

+static bool exclusive_event_match(struct perf_event *e1, struct perf_event *e2)
+{
+ if ((e1->pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE) &&
+ (e1->cpu == e2->cpu ||
+ e1->cpu == -1 ||
+ e2->cpu == -1))
+ return true;
+ return false;
+}
+
+static bool exclusive_event_ok(struct perf_event *event,
+ struct perf_event_context *ctx)
+{
+ struct perf_event *iter_event;
+
+ if (!(event->pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
+ return true;
+
+ list_for_each_entry(iter_event, &ctx->event_list, event_entry) {
+ if (exclusive_event_match(iter_event, event))
+ return false;
+ }
+
+ return true;
+}
+
/**
* sys_perf_event_open - open a performance event, associate it to a task/cpu
*
@@ -7300,6 +7326,11 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_alloc;
}

+ if ((pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE) && group_leader) {
+ err = -EBUSY;
+ goto err_context;
+ }
+
if (task) {
put_task_struct(task);
task = NULL;
@@ -7385,6 +7416,12 @@ SYSCALL_DEFINE5(perf_event_open,
}
}

+ if (!exclusive_event_ok(event, ctx)) {
+ mutex_unlock(&ctx->mutex);
+ fput(event_file);
+ goto err_context;
+ }
+
perf_install_in_context(ctx, event, event->cpu);
perf_unpin_context(ctx);
mutex_unlock(&ctx->mutex);
@@ -7468,6 +7505,14 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,

WARN_ON_ONCE(ctx->parent_ctx);
mutex_lock(&ctx->mutex);
+ if (!exclusive_event_ok(event, ctx)) {
+ mutex_unlock(&ctx->mutex);
+ perf_unpin_context(ctx);
+ put_ctx(ctx);
+ err = -EBUSY;
+ goto err_free;
+ }
+
perf_install_in_context(ctx, event, cpu);
perf_unpin_context(ctx);
mutex_unlock(&ctx->mutex);
--
2.1.0.rc1