Signed-off-by: Vince Weaver <vincent.weaver@xxxxxxxxx> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2 index 504e801..1fc4e27 100644 --- a/man2/perf_event_open.2 +++ b/man2/perf_event_open.2 @@ -654,8 +654,13 @@ Records additional data, if applicable. Usually returned by tracepoint events. .TP .BR PERF_SAMPLE_BRANCH_STACK " (Since Linux 3.4)" -Records the branch stack. -See branch_sample_type. +This provides a record of recent branches, as provided +by CPU branch sampling hardware (such as Intel Last Branch Record). +Not all hardware supports this feature. + +See the +.I branch_sample_type +field for how to filter which branches are reported. .TP .BR PERF_SAMPLE_REGS_USER " (Since Linux 3.7)" Records the current user-level CPU register state @@ -960,8 +965,17 @@ is a further extension of the field. .TP .IR "branch_sample_type" " (Since Linux 3.4)" -This is used with the CPUs hardware branch sampling, if available. -It can have one of the following values: +If +.B PERF_SAMPLE_BRANCH_STACK +is enabled, then this specifies what branches to include +in the branch record. +If the user does not set privilege level explicitly, the kernel +will use the event's privilege level. +Event and branch privilege levels do not have to match. +The value is formed by ORing together zero or more of the following values, +although +.B PERF_SAMPLE_BRANCH_ANY +covers all branch types. .RS .TP .B PERF_SAMPLE_BRANCH_USER @@ -1545,9 +1559,31 @@ is enabled, then a 64-bit value indicating the number of records is included, followed by .I bnr .I perf_branch_entry -structures. -These structures have from, to, and flags values indicating -the from and to addresses from the branches on the callstack. +structures which each include the fields: +.RS +.TP +.I from +indicating the source instruction (may not be a branch) +.TP +.I to +the branch target +.TP +.I mispred +the branch target was mispredicted +.TP +.I predicted +the branch target was predicted. +.RE +The entries are from most to least recent, so the first entry +has the most recent branch. + +Support for +.I mispred +and +.I predicted +is optional; if not supported both +values will be 0. + .TP .IR abi ", " regs[weight(mask)] If -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
