Commits
Wang Nan committed 7fb4b407a12
perf mmap: Don't discard prev in backward mode 'perf record' can switch its output data file. The new output should only store the data after switching. However, in overwrite backward mode, the new output still can have data from before switching. That also brings extra overhead. At the end of mmap_read(), the position of the processed ring buffer is saved in md->prev. Next mmap_read should be end in md->prev if it is not overwriten. That avoids processing duplicate data. However, md->prev is discarded. So next the mmap_read() has to process whole valid ring buffer, which probably includes old processed data. Avoid calling backward_rb_find_range() when md->prev is still available. Signed-off-by: Wang Nan <wangnan0@huawei.com> Tested-by: Kan Liang <kan.liang@intel.com> Acked-by: Namhyung Kim <namhyung@kernel.org> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Mengting Zhang <zhangmengting@huawei.com> Link: http://lkml.kernel.org/r/20171204165107.95327-3-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>