Subject: [PATCH 0/4] Update definition of cmpxchg() under CodeSamples
Hi Paul and Junchang,
Based on the earlier correspondence, I prepared a patch set to update
the definition of cmpxchg().
Patch #1 adds a simple litmus test of cmpxchg().
Patch #2 fix cmpxchg() in .../litmus/api.h by specifying strong
__atomic_compare_exchange_n)\(). Results of litmus tests are presented
in the commit log.
Patch #3 fix cmpxchg() in .../api-gcc.h in the same manner as patch #2.
Patch #4 is not intended to be applied to master, but provides a weak
variant of cmpxchg() and count_lim_atomic_weak.c.
I did some experiments on PPC (10 runs each).
count_lim_atomic 1 uperf, ns/update (as of v2018.12.08a):
56.6572
56.4972
56.5504
56.4972
56.6305
56.5238
56.6038
56.5238
56.5504
56.5238
count_lim_atomic 1 uperf, ns/update (as of Patch #4):
38.3264
38.1073
38.2287
38.2287
38.2653
38.3142
38.1194
38.1801
38.4986
38.2531
count_lim_atomic_weak 1 uperf, ns/update (as of Patch #4):
47.3186
47.3747
47.4121
47.5248
47.3934
47.3373
47.3186
47.4121
47.6002
47.3186
So count_lim_atomic (strong semantics) is around 9ns/update
faster than count_lim_atomic_weak, and is around 18ns/update
faster than count_lim_atomic of v2018.12.08a.
This contradicts Junchang's view. The difference looks like
due to removal of ternary operation in cmpxchg().
Or I might be missing something.
Junchang, can you please experiment on PPC and ARM?
Thanks, Akira
--
Akira Yokosawa (4):
CodeSamples: Add C-cmpxchg.litmus
CodeSamples/formal/litmus/api.h: Fix definition of cmpxchg()
CodeSamples: Fix definition of cmpxchg() in api-gcc.h
[EXP] CodeSamples: Add weak variant of cmpxchg() as cmpxchg_weak()
CodeSamples/api-pthreads/api-gcc.h | 19 ++-
CodeSamples/count/Makefile | 4 +
CodeSamples/count/count_lim_atomic_weak.c | 226 +++++++++++++++++++++++++++++
CodeSamples/formal/litmus/C-cmpxchg.litmus | 24 +++
CodeSamples/formal/litmus/api.h | 2 +-
5 files changed, 272 insertions(+), 3 deletions(-)
create mode 100644 CodeSamples/count/count_lim_atomic_weak.c
create mode 100644 CodeSamples/formal/litmus/C-cmpxchg.litmus
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2.7.4
