Hi List,
i was looking into a ftracetest failure on s390:
# ./ftracetest test.d/trigger/trigger-hist.tc
=== Ftrace unit tests ===
[1] event trigger - test histogram trigger [FAIL]
[2] (instance) event trigger - test histogram trigger [FAIL]
from the -vvv log: ++ fail 'sort param on sched_process_fork did not work'
# cat events/sched/sched_process_fork/hist
# event histogram
#
# trigger info: hist:keys=parent_pid,child_pid:vals=hitcount:sort=child_pid:size=2048 [active]
#
{ parent_pid: 1406, child_pid: 1428 } hitcount: 1
{ parent_pid: 1406, child_pid: 1430 } hitcount: 1
{ parent_pid: 1406, child_pid: 1427 } hitcount: 1
{ parent_pid: 1406, child_pid: 1432 } hitcount: 1
{ parent_pid: 1406, child_pid: 1431 } hitcount: 1
{ parent_pid: 1406, child_pid: 1429 } hitcount: 1
So the test is right, the entries are not sorted. After digging into the
ftrace code i noticed that integer values always get extended to 64 bit
in event_hist_trigger(), but cmp_entries_key() from tracing_map.c uses the
type of the field (which is a pid_t, and therefore 4 bytes).
On Little Endian this doesn't hurt, but on BE s390 this makes the compare
function compare 4 zero bytes, which is the reason why sorting doesn't
work. As a test i forced the compare function used in cmp_entries_key() to
tracing_map_cmp_s64(), which made the ftrace tests pass.
I also tested this on 64 bit parisc with the same results, so the architecture
doesn't seem make a difference (besides LE vs. BE)
Any thoughts on how to fix this? I'm not sure whether i fully understand the
ftrace maps... ;-)
Best,
Sven
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