On 01/05/2017 03:16 AM, Pan Xinhui wrote: > > > 在 2017/1/4 17:41, Peter Zijlstra 写道: >> On Tue, Jan 03, 2017 at 05:07:54PM -0500, Waiman Long wrote: >>> On 01/03/2017 11:18 AM, Peter Zijlstra wrote: >>>> On Sun, Dec 25, 2016 at 03:26:01PM -0500, Waiman Long wrote: >>>>> A number of cmpxchg calls in qspinlock_paravirt.h were replaced by >>>>> more >>>>> relaxed versions to improve performance on architectures that use >>>>> LL/SC. >>>> Claim without numbers ;-) >>> >>> Well it is hard to produce actual numbers here as I don't have the >>> setup >>> to gather data. >> >> Surely RHT has big PPC machines around? I know that getting to them is a >> wee bit of a bother, but they should be available somewhere. >> > hi, > > I do some tests about cmpxchg and cmpxchg_acquire before on ppc. > > loops in 15s of each cmpxchg is below. > > cmpxchg_relaxed: 336663 > cmpxchg_release: 369054 > cmpxchg_acquire: 363364 > cmpxchg: 179435 > > so cmpxchg is really expensive than others. > but I also have doubt about the cmpxchg_relaxed, it should be the > cheapest, but from the tests, release/acquire are faster than it. > > thanks > xinhui > Thanks for doing the test. It looks like we should just focus on using either cmpxchg_release or cmpxchg_acquire and forget about cmpxchg_relaxed.
Cheers, Longman
