The tail position of the event buffer should only be modified after
actually use that event.

If not the event buffer could be invalid before use, and segment fault
occurs when invoking perf top -G.
Signed-off-by: NZhouyi Zhou <yizhouzhou@ict.ac.cn>
Cc: David Ahern <dsahern@gmail.com>
Cc: Zhouyi Zhou <yizhouzhou@ict.ac.cn>
Link: http://lkml.kernel.org/r/1382600613-32177-1-git-send-email-zhouzhouyi@gmail.com
[ Simplified the logic using exit gotos and renamed write_tail method to mmap_consume ]
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

This test case checks frequency conversion of hrtimer-based software
clock events (cpu-clock, task-clock) have valid (non-1) periods.
Signed-off-by: NNamhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1363574507-18808-2-git-send-email-namhyung@kernel.org
[ committer note: Moved .sample_freq to outside named init block to cope with some gcc versions ]
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>