Hi Andrew,
On 26/11/2018 11:12, Andrew Murray wrote:
Many PMU drivers do not have the capability to exclude counting events
that occur in specific contexts such as idle, kernel, guest, etc. These
drivers indicate this by returning an error in their event_init upon
testing the events attribute flags. This approach is error prone and
often inconsistent.
Let's instead allow PMU drivers to advertise their ability to exclude
based on context via a new capability: PERF_PMU_CAP_EXCLUDE. This
allows the perf core to reject requests for exclusion events where
there is no support in the PMU.
Signed-off-by: Andrew Murray <andrew.murray@xxxxxxx>
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 9 +++++++++
2 files changed, 10 insertions(+)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index b2e806f..69b3d65 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -244,6 +244,7 @@ struct perf_event;
#define PERF_PMU_CAP_EXCLUSIVE 0x10
#define PERF_PMU_CAP_ITRACE 0x20
#define PERF_PMU_CAP_HETEROGENEOUS_CPUS 0x40
+#define PERF_PMU_CAP_EXCLUDE 0x80
/**
* struct pmu - generic performance monitoring unit
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5a97f34..9afb33c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9743,6 +9743,15 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
if (ctx)
perf_event_ctx_unlock(event->group_leader, ctx);
+ if (!ret) {
+ if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUDE) &&
+ event_has_any_exclude_flag(event)) {
Technically this is a bisection-breaker, since no driver has this
capability yet - ideally, this patch should come after all the ones
introducing it to the relevant drivers (with the removal of the
now-redundant code from the other drivers at the end).
Alternatively, since we already have several other negative
capabilities, unless there's a strong feeling against adding any more
then it might work out simpler to flip it to PERF_PMU_CAP_NO_EXCLUDE,
such that we only need to introduce the core check then directly replace
the open-coded event checks with the capability in the appropriate
drivers, and need not touch the exclusion-supporting ones at all.
Robin.
+ if (event->destroy)
+ event->destroy(event);
+ ret = -EINVAL;
+ }
+ }
+
if (ret)
module_put(pmu->module);
