Comment 4 for bug 1732651

Hrm, tried this on an s390x VM:

$ uname -a
Linux ckingvm2 4.4.0-101-generic #124-Ubuntu SMP Fri Nov 10 18:29:39 UTC 2017 s390x s390x s390x GNU/Linux

dpkg -l | grep lttng
ii liblttng-ctl0:s390x 2.7.1-2ubuntu1 s390x LTTng control and utility library
ii liblttng-ust-ctl2:s390x 2.7.1-1 s390x LTTng 2.0 Userspace Tracer (trace control library)
ii liblttng-ust-dev:s390x 2.7.1-1 s390x LTTng 2.0 Userspace Tracer (development files)
ii liblttng-ust-python-agent0:s390x 2.7.1-1 s390x LTTng 2.0 Userspace Tracer (Python agent native library)
ii liblttng-ust0:s390x 2.7.1-1 s390x LTTng 2.0 Userspace Tracer (tracing libraries)
ii lttng-modules-dkms 2.8.0-1ubuntu1~16.04.3 all Linux Trace Toolkit (LTTng) kernel modules (DKMS)
ii lttng-tools 2.7.1-2ubuntu1 s390x LTTng control and utility programs

ubuntu@ckingvm2:~$ sudo autotest/client/autotest-local autotest/client/tests/ubuntu_lttng_smoke_test/control
11:29:35 INFO | Writing results to /home/ubuntu/autotest/client/results/default
11:29:35 INFO | START ---- ---- timestamp=1510918175 localtime=Nov 17 11:29:35
11:29:35 INFO | START ubuntu_lttng_smoke_test.lttng-smoke-test ubuntu_lttng_smoke_test.lttng-smoke-test timestamp=1510918175 localtime=Nov 17 11:29:35
11:29:40 ERROR| [stderr] [warning] Tracer discarded 1340 events between [11:29:38.065061128] and [11:29:38.150240071] in trace UUID 6614a11b486b459bce703191741816, at path: "/tmp/lttng-kernel-trace-1494-session/kernel", within stream id 0, at relative path: "channel0_0". You should consider recording a new trace with larger buffers or with fewer events enabled.
11:29:40 INFO | == lttng smoke test of session create/destroy ==
11:29:40 INFO | Session test-kernel-session created.
11:29:40 INFO | Traces will be written in /tmp/lttng-kernel-trace-1494-session
11:29:40 INFO | PASSED (lttng create)
11:29:40 INFO | Session test-kernel-session destroyed
11:29:40 INFO | PASSED (lttng destroy)
11:29:40 INFO |
11:29:40 INFO | == lttng smoke test list kernel events ==
11:29:40 INFO | PASSED (lttng list --kernel)
11:29:40 INFO |
11:29:40 INFO | lttng smoke test trace open/close system calls SKIPPED for s390x
11:29:40 INFO |
11:29:40 INFO | == lttng smoke test trace context switches ==
11:29:40 INFO | Session test-kernel-session created.
11:29:40 INFO | Traces will be written in /tmp/lttng-kernel-trace-1494-session
11:29:40 INFO | PASSED (lttng create)
11:29:40 INFO | Kernel event sched_switch created in channel channel0
11:29:40 INFO | PASSED (lttng enable-event)
11:29:40 INFO | Tracing started for session test-kernel-session
11:29:40 INFO | PASSED (lttng start)
11:29:40 INFO | Waiting for data availability.
11:29:40 INFO | Tracing stopped for session test-kernel-session
11:29:40 INFO | PASSED (lttng stop)
11:29:40 INFO | Session test-kernel-session destroyed
11:29:40 INFO | PASSED (lttng destroy)
11:29:40 INFO | Found 19932 dd and 44645 context switches
11:29:40 INFO | PASSED (simple system call tracing with babeltrace)
11:29:40 INFO |
11:29:40 INFO | Summary: 8 passed, 0 failed
11:29:40 INFO | GOOD ubuntu_lttng_smoke_test.lttng-smoke-test ubuntu_lttng_smoke_test.lttng-smoke-test timestamp=1510918180 localtime=Nov 17 11:29:40 completed successfully
11:29:40 INFO | END GOOD ubuntu_lttng_smoke_test.lttng-smoke-test ubuntu_lttng_smoke_test.lttng-smoke-test timestamp=1510918180 localtime=Nov 17 11:29:40
11:29:40 INFO | END GOOD ---- ---- timestamp=1510918180 localtime=Nov 17 11:29:40
11:29:40 INFO | Report successfully generated at /home/ubuntu/autotest/client/results/default/job_report.html

I just can't seem reproduce this issue.