perf/ring_buffer: Prepare writing into the ring-buffer from the end

Convert perf_output_begin() to __perf_output_begin() and make the later
function able to write records from the end of the ring-buffer.

Following commits will utilize the 'backward' flag.

This is the core patch to support writing to the ring-buffer backwards,
which will be introduced by upcoming patches to support reading from
overwritable ring-buffers.

In theory, this patch should not introduce any extra performance
overhead since we use always_inline, but it does not hurt to double
check that assumption:

When CONFIG_OPTIMIZE_INLINING is disabled, the output object is nearly
identical to original one. See:

   http://lkml.kernel.org/g/[email protected]

When CONFIG_OPTIMIZE_INLINING is enabled, the resuling object file becomes
smaller:

 $ size kernel/events/ring_buffer.o*
   text       data        bss        dec        hex    filename
   4641          4          8       4653       122d kernel/events/ring_buffer.o.old
   4545          4          8       4557       11cd kernel/events/ring_buffer.o.new

Performance testing results:

Calling 3000000 times of 'close(-1)', use gettimeofday() to check
duration.  Use 'perf record -o /dev/null -e raw_syscalls:*' to capture
system calls. In ns.

Testing environment:

 CPU    : Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz
 Kernel : v4.5.0

                     MEAN         STDVAR
  BASE            800214.950    2853.083
  PRE            2253846.700    9997.014
  POST           2257495.540    8516.293

Where 'BASE' is pure performance without capturing. 'PRE' is test
result of pure 'v4.5.0' kernel. 'POST' is test result after this
patch.

Considering the stdvar, this patch doesn't hurt performance, within
noise margin.

For testing details, see:

  http://lkml.kernel.org/g/[email protected]

Signed-off-by: Wang Nan <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Brendan Gregg <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: Zefan Li <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions