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The current code may iterate all the PEBS records in the DS area several times. The first loop is to find all active events and calculate the available records for each event. Then iterate the whole buffer again and again to process available records until all active events are processed. The algorithm is inherited from the old generations. The old PEBS hardware does not deal well with the situation when events happen near each other. SW has to drop the error records. Multiple iterations are required. The hardware limit has been addressed on newer platforms with adaptive PEBS. A simple one-iteration algorithm is introduced. The samples are output by record order with the patch, rather than the event order. It doesn't impact the post-processing. The perf tool always sorts the records by time before presenting them to the end user. In an NMI, the last record has to be specially handled. Add a last[] variable to track the last unprocessed record of each event. Test: 11 PEBS events are used in the perf test. Only the basic information is collected. perf record -e instructions:up,...,instructions:up -c 2000003 benchmark The ftrace is used to record the duration of the intel_pmu_drain_pebs_icl(). The average duration reduced from 62.04us to 57.94us. A small improvement can be observed with the new algorithm. Also, the implementation becomes simpler and more straightforward. Suggested-by: Stephane Eranian <eranian@google.com> Signed-off-by: Kan Liang <kan.liang@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com> Link: https://lore.kernel.org/r/20241119135504.1463839-5-kan.liang@linux.intel.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 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.