trace: Add ring buffer stats to measure rate of events
The stats file under per_cpu folder provides the number of entries, overruns and other statistics about the CPU ring buffer. However, the numbers do not provide any indication of how full the ring buffer is in bytes compared to the overall size in bytes. Also, it is helpful to know the rate at which the cpu buffer is filling up. This patch adds an entry "bytes: " in printed stats for per_cpu ring buffer which provides the actual bytes consumed in the ring buffer. This field includes the number of bytes used by recorded events and the padding bytes added when moving the tail pointer to next page. It also adds the following time stamps: "oldest event ts:" - the oldest timestamp in the ring buffer "now ts:" - the timestamp at the time of reading The field "now ts" provides a consistent time snapshot to the userspace when being read. This is read from the same trace clock used by tracing event timestamps. Together, these values provide the rate at which the buffer is filling up, from the formula: bytes / (now_ts - oldest_event_ts) Signed-off-by:Vaibhav Nagarnaik <vnagarnaik@google.com> Cc: Michael Rubin <mrubin@google.com> Cc: David Sharp <dhsharp@google.com> Link: http://lkml.kernel.org/r/1313531179-9323-3-git-send-email-vnagarnaik@google.com Signed-off-by: