Currently we use perf_event_context::task_ctx_data to save and restore the LBR status when the task is scheduled out and in. We don't allocate it for child contexts, which results in shorter task's LBR stack, because we don't save the history from previous run and start over every time we schedule the task in. I made a test to generate samples with LBR call stack and got higher numbers on bigger chain depths: before: after: LBR call chain: nr: 1 60561 498127 LBR call chain: nr: 2 0 0 LBR call chain: nr: 3 107030 2172 LBR call chain: nr: 4 466685 62758 LBR call chain: nr: 5 2307319 878046 LBR call chain: nr: 6 48713 495218 LBR call chain: nr: 7 1040 4551 LBR call chain: nr: 8 481 172 LBR call chain: nr: 9 878 120 LBR call chain: nr: 10 2377 6698 LBR call chain: nr: 11 28830 151487 LBR call chain: nr: 12 29347 339867 LBR call chain: nr: 13 4 22 LBR call chain: nr: 14 3 53
Unified · Split
| @@ -10703,6 +10703,19 @@ inherit_event(struct perf_event *parent_event, · 10702 unmodified lines | |||
| 10703 | if (IS_ERR(child_event)) | 10703 | if (IS_ERR(child_event)) |
| 10704 | return child_event; | 10704 | return child_event; |
| 10705 | 10705 | ||
| 10706 | |||
| 10707 | if ((child_event->attach_state & PERF_ATTACH_TASK_DATA) && | ||
| 10708 | !child_ctx->task_ctx_data) { | ||
| 10709 | struct pmu *pmu = child_event->pmu; | ||
| 10710 | |||
| 10711 | child_ctx->task_ctx_data = kzalloc(pmu->task_ctx_size, | ||
| 10712 | GFP_KERNEL); | ||
| 10713 | if (!child_ctx->task_ctx_data) { | ||
| 10714 | free_event(child_event); | ||
| 10715 | return NULL; | ||
| 10716 | } | ||
| 10717 | } | ||
| 10718 | |||
| 10706 | /* | 10719 | /* |
| 10707 | * is_orphaned_event() and list_add_tail(&parent_event->child_list) | 10720 | * is_orphaned_event() and list_add_tail(&parent_event->child_list) |
| 10708 | * must be under the same lock in order to serialize against | 10721 | * must be under the same lock in order to serialize against |
| @@ -10713,6 +10726,7 @@ inherit_event(struct perf_event *parent_event, · 4 unmodified lines | |||
| 10713 | if (is_orphaned_event(parent_event) || | 10726 | if (is_orphaned_event(parent_event) || |
| 10714 | !atomic_long_inc_not_zero(&parent_event->refcount)) { | 10727 | !atomic_long_inc_not_zero(&parent_event->refcount)) { |
| 10715 | mutex_unlock(&parent_event->child_mutex); | 10728 | mutex_unlock(&parent_event->child_mutex); |
| 10729 | /* task_ctx_data is freed with child_ctx */ | ||
| 10716 | free_event(child_event); | 10730 | free_event(child_event); |
| 10717 | return NULL; | 10731 | return NULL; |
| 10718 | } | 10732 | } |