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2160d6c8a1
Kernel commit dc4e2801d4 (ring-buffer: Redefine the unimplemented
RINGBUF_TYPE_TIME_STAMP) changed the way the ring buffer timestamps work
- after that commit the previously unimplemented RINGBUF_TYPE_TIME_STAMP
type causes the time delta to be used as a timestamp rather than a delta
to be added to the timestamp.
The trace-cmd code didn't get updated to handle this, so misinterprets
the event data for this case, which causes a cascade of errors,
including trace-report not being able to identify synthetic (or any
other) events generated by the histogram code (which uses TIME_STAMP
mode). For example, the following triggers along with the trace-cmd
shown cause an UNKNOWN_EVENT error and trace-cmd report crash:
# echo 'wakeup_latency u64 lat pid_t pid char comm[16]' > /sys/kernel/debug/tracing/synthetic_events
# echo 'hist:keys=pid:ts0=common_timestamp.usecs if comm=="ping"' > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
# echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_wakeup).trace(wakeup_latency,$wakeup_lat,next_pid,next_comm) if next_comm=="ping"' > /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
# echo 'hist:keys=comm,pid,lat:wakeup_lat=lat:sort=lat' > /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
# trace-cmd record -e wakeup_latency -e sched_wakeup -f comm==\"ping\" ping localhost -c 5
# trace-cmd report
CPU 0 is empty
CPU 1 is empty
CPU 2 is empty
CPU 3 is empty
CPU 5 is empty
CPU 6 is empty
CPU 7 is empty
cpus=8
ug! no event found for type 0
[UNKNOWN TYPE 0]
ug! no event found for type 11520
Segmentation fault (core dumped)
After this patch we get the correct interpretation and the events are
shown properly:
# trace-cmd report
CPU 0 is empty
CPU 1 is empty
CPU 2 is empty
CPU 3 is empty
CPU 5 is empty
CPU 6 is empty
CPU 7 is empty
cpus=8
<idle>-0 [004] 23284.341392: sched_wakeup: ping:12031 [120] success=1 CPU:004
<idle>-0 [004] 23284.341464: wakeup_latency: lat=58, pid=12031, comm=ping
<idle>-0 [004] 23285.365303: sched_wakeup: ping:12031 [120] success=1 CPU:004
<idle>-0 [004] 23285.365382: wakeup_latency: lat=64, pid=12031, comm=ping
<idle>-0 [004] 23286.389290: sched_wakeup: ping:12031 [120] success=1 CPU:004
<idle>-0 [004] 23286.389378: wakeup_latency: lat=72, pid=12031, comm=ping
<idle>-0 [004] 23287.413213: sched_wakeup: ping:12031 [120] success=1 CPU:004
<idle>-0 [004] 23287.413291: wakeup_latency: lat=64, pid=12031, comm=ping
Link: http://lkml.kernel.org/r/1567628224.13841.4.camel@kernel.org
Link: http://lore.kernel.org/linux-trace-devel/20200625100516.365338-3-tz.stoyanov@gmail.com
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
[ Ported from trace-cmd.git ]
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200702185703.785094515@goodmis.org
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.