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4804e01116
Restructure the event opening in perf stat to cycle through the events by CPU after setting affinity to that CPU. This eliminates IPI overhead in the perf API. We have to loop through the CPU in the outter builtin-stat code instead of leaving that to low level functions. It has to change the weak group fallback strategy slightly. Since we cannot easily undo the opens for other CPUs move the weak group retry to a separate loop. Before with a large test case with 94 CPUs: % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 42.75 4.050910 67 60046 110 perf_event_open After: 26.86 0.944396 16 58069 110 perf_event_open (the number changes slightly because the weak group retries work differently and the test case relies on weak groups) Committer notes: Added one of the hunks in a patch provided by Andi after I noticed that the "event times" 'perf test' entry was segfaulting. Signed-off-by: Andi Kleen <ak@linux.intel.com> Acked-by: Jiri Olsa <jolsa@kernel.org> Link: http://lore.kernel.org/lkml/20191121001522.180827-10-andi@firstfloor.org Link: http://lore.kernel.org/lkml/20191127232657.GL84886@tassilo.jf.intel.com # Fix Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
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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.