Re: [PATCH v2 0/7] perf diff: diff cycles at basic block level

[Jiri Olsa <jolsa@redhat.com>]

On Mon, Jun 03, 2019 at 10:36:10PM +0800, Jin Yao wrote:
> 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.

can't compile on Fedora 30

builtin-diff.c: In function ‘block_cycles_diff_cmp’:
builtin-diff.c:544:6: error: absolute value function ‘abs’ given an argument of type ‘s64’ {aka ‘long int’} but has parameter of type ‘int’ which may cause truncation of value [-Werror=absolute-value]
  544 |  l = abs(left->diff.cycles);
      |      ^~~
builtin-diff.c:545:6: error: absolute value function ‘abs’ given an argument of type ‘s64’ {aka ‘long int’} but has parameter of type ‘int’ which may cause truncation of value [-Werror=absolute-value]
  545 |  r = abs(right->diff.cycles);
      |      ^~~

[jolsa@krava perf]$ gcc --version
gcc (GCC) 9.1.1 20190503 (Red Hat 9.1.1-1)

jirka

> 
> With this patch set, for example,
> 
>  # perf record -b ./div
>  # perf record -b ./div
>  # perf diff -s cycles
> 
>  # Event 'cycles'
>  #
>  # Baseline         Block cycles diff [start:end]  Shared Object     Symbol
>  # ........  ....................................  ................  ....................................
>  #
>      49.03%        -9 [         4ef:         520]  div               [.] main
>      49.03%         0 [         4e8:         4ea]  div               [.] main
>      49.03%         0 [         4ef:         500]  div               [.] main
>      49.03%         0 [         4ef:         51c]  div               [.] main
>      49.03%         0 [         4ef:         535]  div               [.] main
>      18.82%         0 [       3ac40:       3ac4d]  libc-2.23.so      [.] __random_r
>      18.82%         0 [       3ac40:       3ac5c]  libc-2.23.so      [.] __random_r
>      18.82%         0 [       3ac40:       3ac76]  libc-2.23.so      [.] __random_r
>      18.82%         0 [       3ac40:       3ac88]  libc-2.23.so      [.] __random_r
>      18.82%         0 [       3ac90:       3ac9c]  libc-2.23.so      [.] __random_r
>      16.29%        -8 [       3aac0:       3aac0]  libc-2.23.so      [.] __random
>      16.29%         0 [       3aac0:       3aad2]  libc-2.23.so      [.] __random
>      16.29%         0 [       3aae0:       3aae7]  libc-2.23.so      [.] __random
>      16.29%         0 [       3ab03:       3ab0f]  libc-2.23.so      [.] __random
>      16.29%         0 [       3ab14:       3ab1b]  libc-2.23.so      [.] __random
>      16.29%         0 [       3ab28:       3ab2e]  libc-2.23.so      [.] __random
>      16.29%         0 [       3ab4a:       3ab53]  libc-2.23.so      [.] __random
>       8.11%         0 [         640:         644]  div               [.] compute_flag
>       8.11%         0 [         649:         659]  div               [.] compute_flag
>       5.46%         0 [       3af60:       3af60]  libc-2.23.so      [.] rand
>       5.46%         0 [       3af60:       3af64]  libc-2.23.so      [.] rand
>       2.25%         0 [         490:         490]  div               [.] rand@plt
>       0.01%        26 [      c00a27:      c00a27]  [kernel.vmlinux]  [k] native_irq_return_iret
>       0.00%      -157 [      2bf9f2:      2bfa63]  [kernel.vmlinux]  [k] update_blocked_averages
>       0.00%       -56 [      2bf980:      2bf9d3]  [kernel.vmlinux]  [k] update_blocked_averages
>       0.00%        48 [      2bf934:      2bf942]  [kernel.vmlinux]  [k] update_blocked_averages
>       0.00%         3 [      2bfb38:      2bfb67]  [kernel.vmlinux]  [k] update_blocked_averages
> 
> The 'cycles' is a new perf-diff computation selection, which enables
> the displaying of cycles difference of same program basic block amongst
> two perf.data. The program basic block is the code block between two
> branches in a function.
> 
>  v2:
>  ---
>  Keep standard perf diff format.
> 
>  Following is the v1 output.
> 
>  # perf diff --basic-block
> 
>  # Cycles diff  Basic block (start:end)
>  # ...........  .......................
>  #
>           -208  hrtimer_interrupt (30b9e0:30ba42)
>           -157  update_blocked_averages (2bf9f2:2bfa63)
>           -126  interrupt_entry (c00880:c0093a)
>            -86  hrtimer_interrupt (30bb29:30bb32)
>            -74  hrtimer_interrupt (30ba65:30bac4)
>            -56  update_blocked_averages (2bf980:2bf9d3)
>             48  update_blocked_averages (2bf934:2bf942)
>            -35  native_write_msr (267900:26790b)
>             26  native_irq_return_iret (c00a27:c00a27)
>             22  rcu_check_callbacks (2febb6:2febdc)
>            -21  __hrtimer_run_queues (30b220:30b2a3)
>             19  pvclock_gtod_notify (14ba0:14c1b)
>            -18  task_tick_fair (2c5d29:2c5d41)
> 
> Jin Yao (7):
>   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: Use hists to manage basic blocks per symbol
>   perf diff: Link same basic blocks among different data files
>   perf diff: Print the basic block cycles diff
>   perf diff: Documentation -c cycles option
> 
>  tools/perf/Documentation/perf-diff.txt |  14 +-
>  tools/perf/builtin-diff.c              | 373 ++++++++++++++++++++++++++++++++-
>  tools/perf/ui/stdio/hist.c             |  26 +++
>  tools/perf/util/hist.c                 |  42 +++-
>  tools/perf/util/hist.h                 |   9 +
>  tools/perf/util/sort.h                 |   8 +
>  tools/perf/util/symbol.c               |  22 ++
>  tools/perf/util/symbol.h               |  23 ++
>  8 files changed, 509 insertions(+), 8 deletions(-)
> 
> -- 
> 2.7.4
>