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The perf mmap'ed buffer contains the flag 'cap_user_time_short' and two extra fields 'time_cycles' and 'time_mask', perf tool needs to know them for handling the counter wrapping case. This patch is to reads out the relevant parameters from the head of the first mmap'ed page and stores into the structure 'perf_tsc_conversion', if the flag 'cap_user_time_short' has been set, it will firstly calibrate cycle value for timestamp calculation. Committer testing: Before/after: # perf test tsc 70: Convert perf time to TSC : Ok # # perf test -v tsc 70: Convert perf time to TSC : --- start --- test child forked, pid 11059 mmap size 528384B 1st event perf time 996384576521 tsc 3850532906613 rdtsc time 996384578455 tsc 3850532913950 2nd event perf time 996384578845 tsc 3850532915428 test child finished with 0 ---- end ---- Convert perf time to TSC: Ok # Signed-off-by: Leo Yan <leo.yan@linaro.org> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Gustavo A. R. Silva <gustavoars@kernel.org> Cc: Ian Rogers <irogers@google.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: John Garry <john.garry@huawei.com> Cc: Kemeng Shi <shikemeng@huawei.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Poirier <mathieu.poirier@linaro.org> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Nick Gasson <nick.gasson@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Remi Bernon <rbernon@codeweavers.com> Cc: Stephane Eranian <eranian@google.com> Cc: Steve Maclean <steve.maclean@microsoft.com> Cc: Will Deacon <will@kernel.org> Cc: Zou Wei <zou_wei@huawei.com> Cc: linux-arm-kernel@lists.infradead.org Link: http://lore.kernel.org/lkml/20200914115311.2201-4-leo.yan@linaro.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.