On Wed, Dec 12, 2018 at 12:39:38AM +0900, Akira Yokosawa wrote: > 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. I applied and pushed #1-3, thank you! Thanx, Paul > 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 > > -- > 2.7.4 >
