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There's a bug in PEBs event enabling code, that prevents PEBS
freq events to work properly after non freq PEBS event was run.
freq events - perf_event_attr::freq set
-F <freq> option of perf record
PEBS events - perf_event_attr::precise_ip > 0
default for perf record
Like in following example with CPU 0 busy, we expect ~10000 samples
for following perf tool run:
# perf record -F 10000 -C 0 sleep 1
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.640 MB perf.data (10031 samples) ]
Everything's fine, but once we run non freq PEBS event like:
# perf record -c 10000 -C 0 sleep 1
[ perf record: Woken up 4 times to write data ]
[ perf record: Captured and wrote 1.053 MB perf.data (20061 samples) ]
the freq events start to fail like this:
# perf record -F 10000 -C 0 sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.185 MB perf.data (40 samples) ]
The issue is in non freq PEBs event initialization of debug_store reset
field, which value is used to auto-reload the counter value after PEBS
event drain. This value is not being used for PEBS freq events, but once
we run non freq event it stays in debug_store data and screws the
sample_freq counting for PEBS freq events.
Setting the reset field to 0 for freq events.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170714163551.19459-1-jolsa@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.