On Wed, 11 Dec 2019 13:33:16 +0100 Sven Schnelle <svens@xxxxxxxxxxxxxx> wrote: > Hi List, Hi Sven, > > 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... ;-) Your analysis makes sense. I'll take a deeper look at it. Thanks for reporting it! -- Steve
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