Commits
Andi Kleen committed 48d02a1d5c1
perf script: Add 'brstackinsn' for branch stacks
Implement printing instruction sequences as hex dump for branch stacks.
This relies on the x86 instruction decoder used by the PT decoder to
find the lengths of instructions to dump them individually.
This is good enough for pattern matching.
This allows to study hot paths for individual samples, together with
branch misprediction and cycle count / IPC information if available (on
Skylake systems).
% perf record -b ...
% perf script -F brstackinsn
...
read_hpet+67:
ffffffff9905b843 insn: 74 ea # PRED
ffffffff9905b82f insn: 85 c9
ffffffff9905b831 insn: 74 12
ffffffff9905b833 insn: f3 90
ffffffff9905b835 insn: 48 8b 0f
ffffffff9905b838 insn: 48 89 ca
ffffffff9905b83b insn: 48 c1 ea 20
ffffffff9905b83f insn: 39 f2
ffffffff9905b841 insn: 89 d0
ffffffff9905b843 insn: 74 ea # PRED
Only works when no special branch filters are specified.
Occasionally the path does not reach up to the sample IP, as the LBRs
may be frozen before executing a final jump. In this case we print a
special message.
The instruction dumper piggy backs on the existing infrastructure from
the IP PT decoder.
An earlier iteration of this patch relied on a disassembler, but this
version only uses the existing instruction decoder.
Committer note:
Added hint about how to get suitable perf.data files for use with
'-F brstackinsm':
$ perf record usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.018 MB perf.data (8 samples) ]
$
$ perf script -F brstackinsn
Display of branch stack assembler requested, but non all-branch filter set
Hint: run 'perf record -b ...'
$
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Link: http://lkml.kernel.org/r/20170223234634.583-1-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>