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perf/core: Add a new PERF_EV_CAP_SIBLING event capability

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Current perf assumes that events in a group are independent. Close an
event doesn't impact the value of the other events in the same group.
If the closed event is a member, after the event closure, other events
are still running like a group. If the closed event is a leader, other
events are running as singleton events.

Add PERF_EV_CAP_SIBLING to allow events to indicate they require being
part of a group, and when the leader dies they cannot exist
independently.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200723171117.9918-8-kan.liang@linux.intel.com
This commit is contained in:
Kan Liang 2020-07-23 10:11:10 -07:00 committed by Peter Zijlstra
parent 58da7dbe6f
commit 9f0c4fa111
2 changed files with 37 additions and 5 deletions
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4
include/linux/perf_event.h
View File

@ -576,9 +576,13 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *,
* 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.
* PERF_EV_CAP_SIBLING: An event with this flag must be a group sibling and
* cannot be a group leader. If an event with this flag is detached from the
* group it is scheduled out and moved into an unrecoverable ERROR state.
*/
#define PERF_EV_CAP_SOFTWARE BIT(0)
#define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1)
#define PERF_EV_CAP_SIBLING BIT(2)
#define SWEVENT_HLIST_BITS 8
#define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)

38
kernel/events/core.c
View File

@ -2133,8 +2133,24 @@ static inline struct list_head *get_event_list(struct perf_event *event)
return event->attr.pinned ? &ctx->pinned_active : &ctx->flexible_active;
}
/*
* Events that have PERF_EV_CAP_SIBLING require being part of a group and
* cannot exist on their own, schedule them out and move them into the ERROR
* state. Also see _perf_event_enable(), it will not be able to recover
* this ERROR state.
*/
static inline void perf_remove_sibling_event(struct perf_event *event)
{
struct perf_event_context *ctx = event->ctx;
struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
event_sched_out(event, cpuctx, ctx);
perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
}
static void perf_group_detach(struct perf_event *event)
{
struct perf_event *leader = event->group_leader;
struct perf_event *sibling, *tmp;
struct perf_event_context *ctx = event->ctx;
@ -2153,7 +2169,7 @@ static void perf_group_detach(struct perf_event *event)
/*
* If this is a sibling, remove it from its group.
*/
if (event->group_leader != event) {
if (leader != event) {
list_del_init(&event->sibling_list);
event->group_leader->nr_siblings--;
goto out;
@ -2166,6 +2182,9 @@ static void perf_group_detach(struct perf_event *event)
*/
list_for_each_entry_safe(sibling, tmp, &event->sibling_list, sibling_list) {
if (sibling->event_caps & PERF_EV_CAP_SIBLING)
perf_remove_sibling_event(sibling);
sibling->group_leader = sibling;
list_del_init(&sibling->sibling_list);
@ -2183,10 +2202,10 @@ static void perf_group_detach(struct perf_event *event)
}
out:
perf_event__header_size(event->group_leader);
for_each_sibling_event(tmp, event->group_leader)
for_each_sibling_event(tmp, leader)
perf_event__header_size(tmp);
perf_event__header_size(leader);
}
static bool is_orphaned_event(struct perf_event *event)
@ -2979,6 +2998,7 @@ static void _perf_event_enable(struct perf_event *event)
raw_spin_lock_irq(&ctx->lock);
if (event->state >= PERF_EVENT_STATE_INACTIVE ||
event->state < PERF_EVENT_STATE_ERROR) {
out:
raw_spin_unlock_irq(&ctx->lock);
return;
}
@ -2990,8 +3010,16 @@ static void _perf_event_enable(struct perf_event *event)
* has gone back into error state, as distinct from the task having
* been scheduled away before the cross-call arrived.
*/
if (event->state == PERF_EVENT_STATE_ERROR)
if (event->state == PERF_EVENT_STATE_ERROR) {
/*
* Detached SIBLING events cannot leave ERROR state.
*/
if (event->event_caps & PERF_EV_CAP_SIBLING &&
event->group_leader == event)
goto out;
event->state = PERF_EVENT_STATE_OFF;
}
raw_spin_unlock_irq(&ctx->lock);
event_function_call(event, __perf_event_enable, NULL);