On Sun, Sep 17, 2017 at 04:05:09PM -0700, Paul E. McKenney wrote: > Hello! >
Hi Paul, > The topic of memory-ordering recipes came up at the Linux Plumbers > Conference microconference on Friday, so I thought that I should summarize > what is currently "out there": > > 1. memory-barriers.txt: A bit rambling and diffuse for a recipes > document. > > 2. > https://www.kernel.org/pub/linux/kernel/people/paulmck/LWNLinuxMM/Examples.html > Many of the examples are on-point, but this is aimed more > at understanding the memory model than at an organized set > of recipes. > > 3. > https://www.kernel.org/pub/linux/kernel/people/paulmck/LWNLinuxMM/Examples.html Duplicate links ;-) This should a link to some slides? > Slides 15-20. Again, some of the litmus tests are on-point, > but the focus is more on understanding the memory model than on > an organized set of recipes. > > So what litmus tests are needed? Here is my initial set: > > 1. Release-acquire chains, AKA ISA2, Z6.2, LB, and 3.LB > > Lots of variety here, can in some cases substitute: > > a. READ_ONCE() for smp_load_acquire() > b. WRITE_ONCE() for smp_store_release() > c. Dependencies for both smp_load_acquire() and > smp_store_release(). > d. smp_wmb() for smp_store_release() in first thread > of ISA2 and Z6.2. > e. smp_rmb() for smp_load_acquire() in last thread of ISA2. > > 2. MP (see test6.pdf for nickname translation) > > a. smp_store_release() / smp_load_acquire() > b. rcu_assign_pointer() / rcu_dereference() > c. smp_wmb() / smp_rmb() > d. Replacing either of the above with smp_mb() > > 3. SB > > a. smp_mb(), as in lockless wait-wakeup coordination. > And as in sys_membarrier()-scheduler coordination, > for that matter. b. replace smp_mb() with smp_mb__before_atomic() followed by a _relaxed cmpchg? As in pv_kick_node(): https://marc.info/?l=linux-kernel&m=150274124711012 Besides, do we also want to add Co* into the set? I think there may be some people still confused to think per-loc SC is not held, and they may add unnecessary barriers in their code. Those (Co*) recipes could serve as a guide for state-machine style programming. Thoughts? Regards, Boqun > > Others? > > Thanx, Paul >
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