In some cases small changes in hot loops can show big differences.
But it's difficult to identify these differences.
perf diff currently can only diff symbols (functions). We can also expand
it to diff cycles of individual programs blocks as reported by timed LBR.
This would allow to identify changes in specific code accurately.
With this patch set, for example,
perf record -b ./div
perf record -b ./div
perf diff --basic-block
# Cycles diff Basic block (start:end)
# ........... .......................
#
-20 native_write_msr (7fff9a069900:7fff9a06990b)
-3 __indirect_thunk_start (7fff9ac02ca0:7fff9ac02ca0)
1 __indirect_thunk_start (7fff9ac02cac:7fff9ac02cb0)
0 rand@plt (490:490)
0 rand (3af60:3af64)
0 rand (3af69:3af6d)
0 main (4e8:4ea)
0 main (4ef:500)
0 main (4ef:535)
0 compute_flag (640:644)
0 compute_flag (649:659)
0 __random_r (3ac40:3ac76)
0 __random_r (3ac40:3ac88)
0 __random_r (3ac90:3ac9c)
0 __random (3aac0:3aad2)
0 __random (3aae0:3aae7)
0 __random (3ab03:3ab0f)
0 __random (3ab14:3ab1b)
0 __random (3ab28:3ab2e)
0 __random (3ab4a:3ab53)
The "basic-block" is a new perf-diff option, which enables the displaying
of cycles difference of same program basic block amongst two or more
perf.data. The program basic block is the code block between two branches
in a function.
Jin Yao (9):
perf util: Create block_info structure
perf util: Add block_info in hist_entry
perf diff: Check if all data files with branch stacks
perf diff: Get a list of symbols(functions)
perf diff: Use hists to manage basic blocks
perf diff: Link same basic blocks among different data files
perf diff: Compute cycles diff of basic blocks
perf diff: Print the basic block cycles diff
perf diff: Documentation --basic-block option
tools/perf/Documentation/perf-diff.txt | 5 +
tools/perf/builtin-diff.c | 521 ++++++++++++++++++++++++++++++++-
tools/perf/util/hist.c | 24 +-
tools/perf/util/hist.h | 6 +
tools/perf/util/sort.h | 4 +
tools/perf/util/symbol.c | 22 ++
tools/perf/util/symbol.h | 23 ++
7 files changed, 594 insertions(+), 11 deletions(-)
--
2.7.4
