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    SubjectRe: [PATCH 2/5] trace: Add ring buffer stats to measure rate of events
    On Fri, Jul 29, 2011 at 11:10 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
    > On Tue, 2011-07-26 at 15:59 -0700, Vaibhav Nagarnaik wrote:
    >> 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:
    >> "head ts:" - the oldest timestamp in the ring buffer
    >
    >
    > I hate the name of "head_ts", as it really is meaningless. The head of
    > our ring buffer is indeed the oldest events, but other ring buffers have
    > head as the newest. This is an internal name that should not be used
    > outside of the ring buffer code itself. Maybe call it "oldest_ts", or
    > even more verbose (and what it actually is), "oldest_event_ts".
    >
    >
    >> "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 - head_ts)
    >>
    >> Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
    >> ---
    >
    >>  /**
    >> + * ring_buffer_head_ts - get the oldest event timestamp from the buffer
    >> + * @buffer: The ring buffer
    >> + * @cpu: The per CPU buffer to read from.
    >> + */
    >> +unsigned long ring_buffer_head_ts(struct ring_buffer *buffer, int cpu)
    >
    > Hence, replace head_ts, with something else here.
    >
    > Thanks,
    >
    > -- Steve
    >

    'oldest_event_ts' sounds good.


    Vaibhav Nagarnaik
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