Hi,
On 2020-01-09 09:48:22 +0100, Jiri Olsa wrote:
On Wed, Jan 08, 2020 at 08:30:30PM -0800, Andres Freund wrote:
Commit 722ddfde366f ("perf tools: Fix time sorting") changed - correctly so - hist_entry__sort to return int64. Unfortunately several of the builtin-c2c.c comparison routines only happened to work due the cast caused by the wrong return type.
This causes meaningless ordering of both the cacheline list, and the cacheline details page. E.g a simple perf c2c record -a sleep 3 perf c2c report will result in cacheline table like ================================================= Shared Data Cache Line Table ================================================= # # ----------- Cacheline ---------- Total Tot ----- LLC Load Hitm ----- ---- Store Reference ---- --- Load Dram ---- LLC Total ----- Core Load Hit ----- -- LLC Load Hit -- # Index Address Node PA cnt records Hitm Total Lcl Rmt Total L1Hit L1Miss Lcl Rmt Ld Miss Loads FB L1 L2 Llc Rmt # ..... .................. .... ...... ....... ....... ....... ....... ....... ....... ....... ....... ........ ........ ....... ....... ....... ....... ....... ........ ........ # 0 0x7f0d27ffba00 N/A 0 52 0.12% 13 6 7 12 12 0 0 7 14 40 4 16 0 0 0 1 0x7f0d27ff61c0 N/A 0 6353 14.04% 1475 801 674 779 779 0 0 718 1392 5574 1299 1967 0 115 0 2 0x7f0d26d3ec80 N/A 0 71 0.15% 16 4 12 13 13 0 0 12 24 58 1 20 0 9 0 3 0x7f0d26d3ec00 N/A 0 98 0.22% 23 17 6 19 19 0 0 6 12 79 0 40 0 10 0 i.e. with the list not being ordered by Total Hitm.
Fixes: 722ddfde366f ("perf tools: Fix time sorting") Signed-off-by: Andres Freund andres@anarazel.de Cc: Jiri Olsa jolsa@kernel.org Cc: Andi Kleen ak@linux.intel.com Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Michael Petlan mpetlan@redhat.com Cc: Namhyung Kim namhyung@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: stable@vger.kernel.org # v3.16+
tools/perf/builtin-c2c.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/tools/perf/builtin-c2c.c b/tools/perf/builtin-c2c.c index e69f44941aad..f2e9d2b1b913 100644 --- a/tools/perf/builtin-c2c.c +++ b/tools/perf/builtin-c2c.c @@ -595,8 +595,8 @@ tot_hitm_cmp(struct perf_hpp_fmt *fmt __maybe_unused, { struct c2c_hist_entry *c2c_left; struct c2c_hist_entry *c2c_right;
- unsigned int tot_hitm_left;
- unsigned int tot_hitm_right;
- uint64_t tot_hitm_left;
- uint64_t tot_hitm_right;
that change looks right, but I can't see how that could happened because of change in Fixes: tag
was the return statement of this function:
return tot_hitm_left - tot_hitm_right;considered to be 'unsigned int' and then converted to int64_t, which would treat negative 'unsigned int' as big positive 'int64_t'?
Correct. So e.g. when comparing 1 and 2 tot_hitm, we'd get (int64_t) UINT_MAX as a result, which is obviously wrong. However, due to hist_entry__sort() returning int at the time, this was masked, as the int64_t was cast to int. Thereby again yielding a negative number for the comparisons of hist_entry__sort()'s result. After hist_entry__sort() was fixed however, there never could be negative return values (but 0's are possible) of hist_entry__sort() for c2c.
I briefly looked for places outside of c2c for similar issues in hist_entry comparison routines, but didn't find any.
Greetings,
Andres Freund