Hi Michael,
On Fri, Jul 13, 2018 at 11:15:26PM +1000, Michael Ellerman wrote: > I reran some numbers today with some slightly updated tests. > > It varies quite a bit across machines and CPU revisions. > > On one I get: > > Lock/Unlock Time Time % Total Cycles Cycles Cycles > Delta > lwsync/lwsync 79,290,859,955 100.0 % 290,160,065,087 145 - > lwsync/sync 104,903,703,237 132.3 % 383,966,199,430 192 47 > > Another: > > Lock/Unlock Time Time % Total Cycles Cycles Cycles > Delta > lwsync/lwsync 71,662,395,722 100.0 % 252,403,777,715 126 - > lwsync/sync 84,932,987,977 118.5 % 299,141,951,285 150 23 > > > So 18-32% slower, or 23-47 cycles. Very good info. Note that another option is to put the SYNC in lock() it doesn't really matter which of the two primitives gets it. I don't suppose it really matters for timing either way around. > Next week I can do some macro benchmarks, to see if it's actually > detectable at all. > > The other question is how they behave on a heavily loaded system. > > > My personal preference would be to switch to sync, we don't want to be > the only arch finding (or not finding!) exotic ordering bugs. > > But we'd also rather not make our slow locks any slower than they have > to be. I completely understand, but I'll get you beer (lots) if you do manage to make SYNC happen :-) :-)
