From: Kan Liang <[email protected]> In LBR call stack mode, the depth of reconstructed LBR call stack limits to the number of LBR registers. With LBR Top-of-Stack (TOS) 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 LBR TOS. Only when the new branch sample type is set, the TOS 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 <[email protected]> --- include/linux/perf_event.h | 2 ++ include/uapi/linux/perf_event.h | 10 +++++++++- kernel/events/core.c | 11 +++++++++++ 3 files changed, 22 insertions(+), 1 deletion(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 61448c19a132..2b229ea1cc15 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -92,6 +92,7 @@ struct perf_raw_record { /* * branch stack layout: * nr: number of taken branches stored in entries[] + * tos: Top-of-Stack (TOS) information. PMU specific data. * * Note that nr can vary from sample to sample * branches (to, from) are stored from most recent @@ -100,6 +101,7 @@ struct perf_raw_record { */ struct perf_branch_stack { __u64 nr; + __u64 tos; /* PMU specific data */ struct perf_branch_entry entries[0]; }; diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index bb7b271397a6..b1f022190571 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -180,6 +180,8 @@ enum perf_branch_sample_type_shift { PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT = 16, /* save branch type */ + PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT = 17, /* save LBR TOS */ + PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */ }; @@ -207,6 +209,8 @@ enum perf_branch_sample_type { PERF_SAMPLE_BRANCH_TYPE_SAVE = 1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT, + PERF_SAMPLE_BRANCH_LBR_TOS = 1U << PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT, + PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT, }; @@ -849,7 +853,11 @@ enum perf_event_type { * char data[size];}&& PERF_SAMPLE_RAW * * { u64 nr; - * { u64 from, to, flags } lbr[nr];} && PERF_SAMPLE_BRANCH_STACK + * { u64 from, to, flags } lbr[nr]; + * + * # only available if PERF_SAMPLE_BRANCH_LBR_TOS is set + * u64 tos; + * } && PERF_SAMPLE_BRANCH_STACK * * { u64 abi; # enum perf_sample_regs_abi * u64 regs[weight(mask)]; } && PERF_SAMPLE_REGS_USER diff --git a/kernel/events/core.c b/kernel/events/core.c index 9ec0b0bfddbd..18b0a7d2c67e 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6343,6 +6343,11 @@ static void perf_output_read(struct perf_output_handle *handle, perf_output_read_one(handle, event, enabled, running); } +static inline bool perf_sample_save_lbr_tos(struct perf_event *event) +{ + return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_LBR_TOS; +} + void perf_output_sample(struct perf_output_handle *handle, struct perf_event_header *header, struct perf_sample_data *data, @@ -6432,6 +6437,8 @@ void perf_output_sample(struct perf_output_handle *handle, perf_output_put(handle, data->br_stack->nr); perf_output_copy(handle, data->br_stack->entries, size); + if (perf_sample_save_lbr_tos(event)) + perf_output_put(handle, data->br_stack->tos); } else { /* * we always store at least the value of nr @@ -6619,7 +6626,11 @@ void perf_prepare_sample(struct perf_event_header *header, if (data->br_stack) { size += data->br_stack->nr * sizeof(struct perf_branch_entry); + + if (perf_sample_save_lbr_tos(event)) + size += sizeof(u64); } + header->size += size; } -- 2.17.1
