perf cs-etm: Remove callback cs_etm_find_snapshot()

The callback cs_etm_find_snapshot() is invoked for snapshot mode, its
main purpose is to find the correct AUX trace data and returns "head"
and "old" (we can call "old" as "old head") to the caller, the caller
__auxtrace_mmap__read() uses these two pointers to decide the AUX trace
data size.

This patch removes cs_etm_find_snapshot() with below reasons:

- The first thing in cs_etm_find_snapshot() is to check if the head has
  wrapped around, if it is not, directly bails out.  The checking is
  pointless, this is because the "head" and "old" pointers both are
  monotonical increasing so they never wrap around.

- cs_etm_find_snapshot() adjusts the "head" and "old" pointers and
  assumes the AUX ring buffer is fully filled with the hardware trace
  data, so it always subtracts the difference "mm->len" from "head" to
  get "old".  Let's imagine the snapshot is taken in very short
  interval, the tracers only fill a small chunk of the trace data into
  the AUX ring buffer, in this case, it's wrongly to copy the whole the
  AUX ring buffer to perf file.

- As the "head" and "old" pointers are monotonically increased, the
  function __auxtrace_mmap__read() handles these two pointers properly.
  It calculates the reminders for these two pointers, and the size is
  clamped to be never more than "snapshot_size".  We can simply reply on
  the function __auxtrace_mmap__read() to calculate the correct result
  for data copying, it's not necessary to add Arm CoreSight specific
  callback.

Signed-off-by: Leo Yan <[email protected]>
Reviewed-by: James Clark <[email protected]>
Tested-by: James Clark <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Daniel Kiss <[email protected]>
Cc: Denis Nikitin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Garry <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Poirier <[email protected]>
Cc: Mike Leach <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Suzuki Poulouse <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

0 files changed, 0 insertions, 0 deletions