Introduce the flag PMU_EV_CAP_READ_ACTIVE_PKG, useful for uncore events,
that allows a PMU to signal the generic perf code that an event is readable
in the current CPU if the event is active in a CPU in the same package as
the current CPU.
This is an optimization that avoids a unnecessary IPI for the common case
where uncore events are run and read in the same package but in
different CPUs.
As an example, the IPI removal speeds up perf_read in my Haswell system
as follows:
- For event UNC_C_LLC_LOOKUP: From 260 us to 31 us.
- For event RAPL's power/energy-cores/: From to 255 us to 27 us.
For the optimization to work, all events in the group must have it
(similarly to PERF_EV_CAP_SOFTWARE).
Signed-off-by: David Carrillo-Cisneros <davi...@google.com>
---
include/linux/perf_event.h | 3 +++
kernel/events/core.c | 32 +++++++++++++++++++++++++-------
2 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index fa5617f..c8bb1b3 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -501,8 +501,11 @@ typedef void (*perf_overflow_handler_t)(struct perf_event
*,
* Event capabilities. For event_caps and groups caps.
*
* PERF_EV_CAP_SOFTWARE: Is a software event.
+ * PERF_EV_CAP_READ_ACTIVE_PKG: A CPU event (or cgroup event) that can be read
+ * from any CPU in the package where it is active.
*/
#define PERF_EV_CAP_SOFTWARE BIT(0)
+#define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1)
#define SWEVENT_HLIST_BITS 8
#define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 34049cc..77f1bd3 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3333,6 +3333,26 @@ struct perf_read_data {
int ret;
};
+static int find_cpu_to_read(struct perf_event *event)
+{
+ bool active = event->state == PERF_EVENT_STATE_ACTIVE;
+ int event_cpu = event->oncpu, local_cpu = smp_processor_id();
+ u16 local_pkg, event_pkg;
+
+ if (!active)
+ return -1;
+
+ if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
+ event_pkg = topology_physical_package_id(event_cpu);
+ local_pkg = topology_physical_package_id(local_cpu);
+
+ if (event_pkg == local_pkg)
+ return local_cpu;
+ }
+
+ return event_cpu;
+}
+
/*
* Cross CPU call to read the hardware event
*/
@@ -3454,19 +3474,17 @@ u64 perf_event_read_local(struct perf_event *event)
static int perf_event_read(struct perf_event *event, bool group)
{
- int ret = 0;
+ int ret = 0, cpu_to_read;
- /*
- * If event is enabled and currently active on a CPU, update the
- * value in the event structure:
- */
- if (event->state == PERF_EVENT_STATE_ACTIVE) {
+ cpu_to_read = find_cpu_to_read(event);
+
+ if (cpu_to_read >= 0) {
struct perf_read_data data = {
.event = event,
.group = group,
.ret = 0,
};
- ret = smp_call_function_single(event->oncpu,
+ ret = smp_call_function_single(cpu_to_read,
__perf_event_read, &data, 1);
ret = ret ? : data.ret;
} else if (event->state == PERF_EVENT_STATE_INACTIVE) {
--
2.8.0.rc3.226.g39d4020
