From 313ccb96159489eabdbdcf4deb34e7fbac17557d Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Sun, 7 Jan 2018 17:03:47 +0100 Subject: [PATCH] perf: Allocate context task_ctx_data for child event 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 Signed-off-by: Jiri Olsa Acked-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Andi Kleen Cc: David Ahern Cc: Namhyung Kim Fixes: 4af57ef28c2c ("perf: Add pmu specific data for perf task context") Link: http://lkml.kernel.org/r/20180107160356.28203-4-jolsa@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- kernel/events/core.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index 4df5b695bf0d..55fb648a32b0 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10703,6 +10703,19 @@ inherit_event(struct perf_event *parent_event, if (IS_ERR(child_event)) return child_event; + + if ((child_event->attach_state & PERF_ATTACH_TASK_DATA) && + !child_ctx->task_ctx_data) { + struct pmu *pmu = child_event->pmu; + + child_ctx->task_ctx_data = kzalloc(pmu->task_ctx_size, + GFP_KERNEL); + if (!child_ctx->task_ctx_data) { + free_event(child_event); + return NULL; + } + } + /* * is_orphaned_event() and list_add_tail(&parent_event->child_list) * must be under the same lock in order to serialize against @@ -10713,6 +10726,7 @@ inherit_event(struct perf_event *parent_event, if (is_orphaned_event(parent_event) || !atomic_long_inc_not_zero(&parent_event->refcount)) { mutex_unlock(&parent_event->child_mutex); + /* task_ctx_data is freed with child_ctx */ free_event(child_event); return NULL; } -- 2.45.2