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SubjectRe: [PATCH] perf documentation: Add desription forHEADER_TRACING_DATA
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On 3/11/20 2:58 PM, Arnaldo Carvalho de Melo wrote:
> Em Tue, Mar 03, 2020 at 08:08:46AM +0100, Thomas Richter escreveu:
>> Add description and layout in the perf.data file for
>> the header part describing trace data used in commands
>> perf record -e XXX
>> where XXX is a probe or tracepoint.
>
> Did you write this from scratch? I was going thru it and couldn't find
> what that "Note member 'ftrace_count' can be zero." refers to, couldn't
> find this ftrace_counter, is this outdated?
>
> [root@five ~]# find /sys/kernel/debug/tracing/events/ -type f | xargs grep ftrace_count
> [root@five ~]# find /sys/kernel/debug/tracing/events/ -name ftrace_count
> [root@five ~]# uname -a
> Linux five 5.5.5-200.fc31.x86_64 #1 SMP Wed Feb 19 23:28:07 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
> [root@five ~]#
>
> The part about using a probe and then go on dissecting it is really
> nice, I'll try reproducing it soon,
>
> Thanks,
>

Arnaldo,

yes, I wrote this from scratch. I decided to invest some time into the
documentation after I have spent nearly 3 week in debugging why commands

perf record -e probe:vfs_getname

followed by

perf report

did not print the file name on s390. Remember we talked about failing
test case 65: Check open filename arg using perf trace + vfs_getname.
(Steven Rostedt and Masami Hiramatsu helped me on this).

On ftrace_count: This is not a file available in /sys/kernel/debug/tracing.
It is a value saved in function

tracing_data_get
record_ftrace_files
copy_event_system --> Check for some format file in directories
/sys/kernel/debug/tracing/events/ftrace/*/
Depending on what probe was defined, there is no hit and zero is written
to the output.

Hope this helps.
--
Thomas Richter, Dept 3252, IBM s390 Linux Development, Boeblingen, Germany
--
Vorsitzender des Aufsichtsrats: Matthias Hartmann
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294

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