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perf_event_open.2: Add cycles field in LBR records 

Linux 4.3 (71ef3c6b9d4665ee7afbbe4c208a98917dcfc32f)
added a cycles field to the PERF_SAMPLE_BRANCH_STACK
last branch records.

The kernel commit was a bit vague on this, but you can find
a few more details on this in the Intel Architectural Manual
vol3B.  The field indicates the number of core cycles elapsed
since the previous update to the LBR stack.

This feature is only found on Skylake and newer Intel chips,
as well as Intel Atom Goldmont chips.  I'm not sure if it's
worth adding this info to the manpage, as it seems a bit
specific and will probably get rapidly out of date.

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
This commit is contained in:
Vince Weaver 2016-10-19 11:10:53 -04:00 committed by Michael Kerrisk
parent 54905b0fc3
commit 9691959295
1 changed files with 7 additions and 4 deletions
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man2/perf_event_open.2
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@ -2183,15 +2183,18 @@ The branch was in a transactional memory transaction.
.IR abort " (since Linux 3.11)"
.\" commit 135c5612c460f89657c4698fe2ea753f6f667963
The branch was in an aborted transactional memory transaction.
.TP
.IR cycles " (since Linux 4.3)"
.\" commit 71ef3c6b9d4665ee7afbbe4c208a98917dcfc32f
This reports the number of cycles elapsed since the
previous branch stack update.
.P
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
.IR mispred ", " predicted " and " cycles
is optional; if not supported, those
values will be 0.
The type of branches recorded is specified by the