On Mon, Mar 28, 2016 at 06:41:31AM +0000, Wang Nan wrote: > 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 ring buffer backward, which > would be introduced by following patch to support reading from > overwritable ring buffer. > > In theory, this patch should not introduce any extra performance > overhead since we use always_inline. > > When CONFIG_OPTIMIZE_INLINING is disabled, the output object is nearly > identical to original one. See [1]. > > When CONFIG_OPTIMIZE_INLINING is enabled, the resuling object file becomes > smaller: > > $ size kernel/events/ring_buffer.o* > text data bss dec hex filename > 4545 4 8 4557 11cd > kernel/events/ring_buffer.o.new > 4641 4 8 4653 122d > kernel/events/ring_buffer.o.old > > Performance result: > > 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. See [4] for detail experimental setup. > > Considering the stdvar, this patch doesn't hurt performance. > > For the detail of testing method, please refer to [2]. > > [1] http://lkml.kernel.org/g/56f52e83.70...@huawei.com > [2] http://lkml.kernel.org/g/56f89dcd.1040...@huawei.com > > Signed-off-by: Wang Nan <wangn...@huawei.com> > Cc: He Kuang <heku...@huawei.com> > Cc: Alexei Starovoitov <a...@kernel.org> > Cc: Arnaldo Carvalho de Melo <a...@redhat.com> > Cc: Brendan Gregg <brendan.d.gr...@gmail.com> > Cc: Jiri Olsa <jo...@kernel.org> > Cc: Masami Hiramatsu <masami.hiramatsu...@hitachi.com> > Cc: Namhyung Kim <namhy...@kernel.org> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Zefan Li <lize...@huawei.com> > Cc: pi3or...@163.com > --- > kernel/events/ring_buffer.c | 42 ++++++++++++++++++++++++++++++++++++------ > 1 file changed, 36 insertions(+), 6 deletions(-)
Acked-by: Alexei Starovoitov <a...@kernel.org>
