On Fri, May 22, 2020 at 10:32:01AM -0400, Alan Stern wrote: > On Fri, May 22, 2020 at 11:44:07AM +0200, Peter Zijlstra wrote: > > On Thu, May 21, 2020 at 05:38:50PM -0700, Paul E. McKenney wrote: > > > Hello! > > > > > > Just wanted to call your attention to some pretty cool and pretty serious > > > litmus tests that Andrii did as part of his BPF ring-buffer work: > > > > > > https://lore.kernel.org/bpf/20200517195727.279322-3-andriin@xxxxxx/ > > > > > > Thoughts? > > > > I find: > > > > smp_wmb() > > smp_store_release() > > > > a _very_ weird construct. What is that supposed to even do? > > Indeed, it looks like one or the other of those is redundant (depending > on the context). Probably. Peter instead asked what it was supposed to even do. ;-) > Also, what use is a spinlock that is accessed in only one thread? Multiple writers synchronize via the spinlock in this case. I am guessing that his larger 16-hour test contended this spinlock. > Finally, I doubt that these tests belong under tools/memory-model. > Shouldn't they go under the new Documentation/ directory for litmus > tests? And shouldn't the patch update a README file? Agreed, and I responded to that effect to his original patch: https://lore.kernel.org/bpf/20200522003433.GG2869@paulmck-ThinkPad-P72/ Thanx, Paul
