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Levi Yun b746a3afa2 trace/trace_event_perf: remove duplicate samples on the first tracepoint event 
[ Upstream commit afe5960dc2 ]

When a tracepoint event is created with attr.freq = 1,
'hwc->period_left' is not initialized correctly. As a result,
in the perf_swevent_overflow() function, when the first time the event occurs,
it calculates the event overflow and the perf_swevent_set_period() returns 3,
this leads to the event are recorded for three duplicate times.

Step to reproduce:
    1. Enable the tracepoint event & starting tracing
         $ echo 1 > /sys/kernel/tracing/events/module/module_free
         $ echo 1 > /sys/kernel/tracing/tracing_on

    2. Record with perf
         $ perf record -a --strict-freq -F 1 -e "module:module_free"

    3. Trigger module_free event.
         $ modprobe -i sunrpc
         $ modprobe -r sunrpc

Result:
     - Trace pipe result:
         $ cat trace_pipe
         modprobe-174509  [003] .....  6504.868896: module_free: sunrpc

     - perf sample:
         modprobe  174509 [003]  6504.868980: module:module_free: sunrpc
         modprobe  174509 [003]  6504.868980: module:module_free: sunrpc
         modprobe  174509 [003]  6504.868980: module:module_free: sunrpc

By setting period_left via perf_swevent_set_period() as other sw_event did,
This problem could be solved.

After patch:
     - Trace pipe result:
         $ cat trace_pipe
         modprobe 1153096 [068] 613468.867774: module:module_free: xfs

     - perf sample
         modprobe 1153096 [068] 613468.867794: module:module_free: xfs

Link: https://lore.kernel.org/20240913021347.595330-1-yeoreum.yun@arm.com
Fixes: bd2b5b1284 ("perf_counter: More aggressive frequency adjustment")
Signed-off-by: Levi Yun <yeoreum.yun@arm.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2024-12-05 14:02:02 +01:00
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README 

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 reStructuredText 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.