On Sun, Jan 07, 2018 at 05:03:47PM +0100, Jiri Olsa wrote: > 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
Acked-by: Peter Zijlstra (Intel) <[email protected]> Fixes: 4af57ef28c2c ("perf: Add pmu specific data for perf task context") > Cc: Andi Kleen <[email protected]> > Signed-off-by: Jiri Olsa <[email protected]> > --- > 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; > } > -- > 2.13.6 >
