[PATCH v5 0/9] perf: Refine barriers for AUX ring buffer

[Leo Yan]

This patch series is to refine the memory barriers for AUX ring buffer.

Patches 01 ~ 04 to address the barriers usage in the kernel.  The first
patch is to make clear comment for how to use the barriers between the
data store and aux_head store, this asks the driver to make sure the
data is visible.  Patches 02 ~ 04 is to refine the drivers for barriers
after the data store.

Patch 05 is to use WRITE_ONCE() for updating aux_tail.

Patches 06 ~ 09 is to drop the legacy __sync functions, and polish for
duplicate code and cleanup the build and feature test after
SYNC_COMPARE_AND_SWAP is not used.

For easier review and more clear patch organization, comparing against
to the previous patch series, the patches for support compat mode for
AUX trace have been left out and will be sent out as a separate patch
set.

This patch set have been tested on Arm64 Juno platform.

Changes from v4:
- Refined comment for CoreSight ETR/ETF drivers (Suzuki/Peter);
- Changed to use compiler barrier for BTS (mentioned by Peter, but have
  not received response from Intel developer);
- Refined the coding style for patch 07 (Adrian).

Changes from v3:
- Removed the inapprocate paragraph in the commit log for patch "perf
  auxtrace: Drop legacy __sync functions" (Adrian);
- Added new patch to remove feature-sync-compare-and-swap test (Adrian);
- Th patch for "perf auxtrace: Use WRITE_ONCE() for updating aux_tail",
  is a standlone and simple change, so moved it ahead in the patch set
  for better ordering;
- Minor improvement for commit logs in the last two patches.

Changes from v2:
- Removed auxtrace_mmap__read_snapshot_head(), which has the duplicated
  code with auxtrace_mmap__read_head();
- Cleanuped the build for HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT (Adrian);
- Added global variable "kernel_is_64_bit" (Adrian);
- Added compat variants compat_auxtrace_mmap__{read_head|write_tail}
  (Adrian).


Leo Yan (9):
  perf/ring_buffer: Add comment for barriers on AUX ring buffer
  coresight: tmc-etr: Add barrier after updating AUX ring buffer
  coresight: tmc-etf: Add comment for store ordering
  perf/x86: Add compiler barrier after updating BTS
  perf auxtrace: Use WRITE_ONCE() for updating aux_tail
  perf auxtrace: Drop legacy __sync functions
  perf auxtrace: Remove auxtrace_mmap__read_snapshot_head()
  perf: Cleanup for HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT
  tools: Remove feature-sync-compare-and-swap feature detection

 arch/x86/events/intel/bts.c                   |  6 ++++
 .../hwtracing/coresight/coresight-tmc-etf.c   |  5 +++
 .../hwtracing/coresight/coresight-tmc-etr.c   |  8 +++++
 kernel/events/ring_buffer.c                   |  9 ++++++
 tools/build/Makefile.feature                  |  1 -
 tools/build/feature/Makefile                  |  4 ---
 tools/build/feature/test-all.c                |  4 ---
 .../feature/test-sync-compare-and-swap.c      | 15 ---------
 tools/perf/Makefile.config                    |  4 ---
 tools/perf/util/auxtrace.c                    | 18 +++--------
 tools/perf/util/auxtrace.h                    | 31 +------------------
 11 files changed, 34 insertions(+), 71 deletions(-)
 delete mode 100644 tools/build/feature/test-sync-compare-and-swap.c

-- 
2.25.1