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SubjectRe: [PATCH] perf documentation: Add desription forHEADER_TRACING_DATA
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 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 find this ftrace_counter, is this outdated?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,


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

copy_event_system --> Check for some format file in directories
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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