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perf_event_open.2: Improve PERF_SAMPLE_BRANCH_STACK documentation 

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Vince Weaver 2013-07-08 15:47:05 -04:00 committed by Michael Kerrisk
parent a877cf9226
commit 045bf4d3db
1 changed files with 43 additions and 7 deletions
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man2/perf_event_open.2
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@ -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