From bbfd5e4fab63703375eafaf241a0c696024a59e1 Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Mon, 27 Jan 2020 08:53:54 -0800 Subject: perf/core: Add new branch sample type for HW index of raw branch records The low level index is the index in the underlying hardware buffer of the most recently captured taken branch which is always saved in branch_entries[0]. It is very useful for reconstructing the call stack. For example, in Intel LBR call stack mode, the depth of reconstructed LBR call stack limits to the number of LBR registers. With the low level index information, perf tool may stitch the stacks of two samples. The reconstructed LBR call stack can break the HW limitation. Add a new branch sample type to retrieve low level index of raw branch records. The low level index is between -1 (unknown) and max depth which can be retrieved in /sys/devices/cpu/caps/branches. Only when the new branch sample type is set, the low level index information is dumped into the PERF_SAMPLE_BRANCH_STACK output. Perf tool should check the attr.branch_sample_type, and apply the corresponding format for PERF_SAMPLE_BRANCH_STACK samples. Otherwise, some user case may be broken. For example, users may parse a perf.data, which include the new branch sample type, with an old version perf tool (without the check). Users probably get incorrect information without any warning. Signed-off-by: Kan Liang Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20200127165355.27495-2-kan.liang@linux.intel.com --- kernel/events/core.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'kernel/events') diff --git a/kernel/events/core.c b/kernel/events/core.c index e453589da97c..3f1f77de7247 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6555,6 +6555,11 @@ static void perf_output_read(struct perf_output_handle *handle, perf_output_read_one(handle, event, enabled, running); } +static inline bool perf_sample_save_hw_index(struct perf_event *event) +{ + return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_HW_INDEX; +} + void perf_output_sample(struct perf_output_handle *handle, struct perf_event_header *header, struct perf_sample_data *data, @@ -6643,6 +6648,8 @@ void perf_output_sample(struct perf_output_handle *handle, * sizeof(struct perf_branch_entry); perf_output_put(handle, data->br_stack->nr); + if (perf_sample_save_hw_index(event)) + perf_output_put(handle, data->br_stack->hw_idx); perf_output_copy(handle, data->br_stack->entries, size); } else { /* @@ -6836,6 +6843,9 @@ void perf_prepare_sample(struct perf_event_header *header, if (sample_type & PERF_SAMPLE_BRANCH_STACK) { int size = sizeof(u64); /* nr */ if (data->br_stack) { + if (perf_sample_save_hw_index(event)) + size += sizeof(u64); + size += data->br_stack->nr * sizeof(struct perf_branch_entry); } -- cgit v1.2.3-70-g09d2