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Subject[PATCH v3 2/4] perf/core: generalize event->group_flags
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Currently, PERF_GROUP_SOFTWARE is used in the group_flags field of a
group's leader to indicate that is_software_event(event) is true for all
events in a group. This is the only usage of event->group_flags.

This pattern of setting a group level flags when all events in the group
share a property is useful for the flag introduced in the next patch and
for future CQM/CMT flags. So this patches generalizes group_flags to work
as an aggregate of event level flags.

PERF_GROUP_SOFTWARE denotes an inmutable event's property. All other flags
that I intend to add are also determinable at event initialization.
To better convey the above, this patch renames event's group_flags to
group_caps and PERF_GROUP_SOFTWARE to PERF_EV_CAP_SOFTWARE.

Individual event flags are stored in the new event->event_caps. Since the
cap flags do not change after event initialization, there is no need to
serialize event_caps. This new field is used when events are added to a
context, similarly to how PERF_GROUP_SOFTWARE and is_software_event()
worked.

Lastly, for consistency, updates is_software_event() to rely in event_cap
instead of the context index.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
include/linux/perf_event.h | 18 +++++++++++++-----
kernel/events/core.c | 16 ++++++++--------
2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 529c41f..6f7459f 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -510,9 +510,12 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *,
struct perf_sample_data *,
struct pt_regs *regs);

-enum perf_group_flag {
- PERF_GROUP_SOFTWARE = 0x1,
-};
+/*
+ * Event capabilities. For event_caps and groups caps.
+ *
+ * PERF_EV_CAP_SOFTWARE: Is a software event.
+ */
+#define PERF_EV_CAP_SOFTWARE BIT(0)

#define SWEVENT_HLIST_BITS 8
#define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)
@@ -568,7 +571,12 @@ struct perf_event {
struct hlist_node hlist_entry;
struct list_head active_entry;
int nr_siblings;
- int group_flags;
+
+ /* Not serialized. Only written during event initialization. */
+ int event_caps;
+ /* The cumulative AND of all event_caps for events in this group. */
+ int group_caps;
+
struct perf_event *group_leader;
struct pmu *pmu;
void *pmu_private;
@@ -988,7 +996,7 @@ static inline bool is_sampling_event(struct perf_event *event)
*/
static inline int is_software_event(struct perf_event *event)
{
- return event->pmu->task_ctx_nr == perf_sw_context;
+ return event->event_caps & PERF_EV_CAP_SOFTWARE;
}

extern struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 35afbfa..5b83509 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1439,8 +1439,7 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
if (event->group_leader == event) {
struct list_head *list;

- if (is_software_event(event))
- event->group_flags |= PERF_GROUP_SOFTWARE;
+ event->group_caps = event->event_caps;

list = ctx_group_list(event, ctx);
list_add_tail(&event->group_entry, list);
@@ -1594,9 +1593,7 @@ static void perf_group_attach(struct perf_event *event)

WARN_ON_ONCE(group_leader->ctx != event->ctx);

- if (group_leader->group_flags & PERF_GROUP_SOFTWARE &&
- !is_software_event(event))
- group_leader->group_flags &= ~PERF_GROUP_SOFTWARE;
+ group_leader->group_caps &= event->event_caps;

list_add_tail(&event->group_entry, &group_leader->sibling_list);
group_leader->nr_siblings++;
@@ -1687,7 +1684,7 @@ static void perf_group_detach(struct perf_event *event)
sibling->group_leader = sibling;

/* Inherit group flags from the previous leader */
- sibling->group_flags = event->group_flags;
+ sibling->group_caps = event->group_caps;

WARN_ON_ONCE(sibling->ctx != event->ctx);
}
@@ -2113,7 +2110,7 @@ static int group_can_go_on(struct perf_event *event,
/*
* Groups consisting entirely of software events can always go on.
*/
- if (event->group_flags & PERF_GROUP_SOFTWARE)
+ if (event->group_caps & PERF_EV_CAP_SOFTWARE)
return 1;
/*
* If an exclusive group is already on, no other hardware
@@ -9450,6 +9447,9 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_alloc;
}

+ if (pmu->task_ctx_nr == perf_sw_context)
+ event->event_caps |= PERF_EV_CAP_SOFTWARE;
+
if (group_leader &&
(is_software_event(event) != is_software_event(group_leader))) {
if (is_software_event(event)) {
@@ -9463,7 +9463,7 @@ SYSCALL_DEFINE5(perf_event_open,
*/
pmu = group_leader->pmu;
} else if (is_software_event(group_leader) &&
- (group_leader->group_flags & PERF_GROUP_SOFTWARE)) {
+ (group_leader->group_caps & PERF_EV_CAP_SOFTWARE)) {
/*
* In case the group is a pure software group, and we
* try to add a hardware event, move the whole group to
--
2.8.0.rc3.226.g39d4020
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