On Tue, Nov 17, 2015 at 05:07:38PM +0530, Vineet Gupta wrote: > > as is ARC-SMP seems to have a _lot_ of superfluous > > barriers many of which have no explanation yet (I'm thinking of those > > extra smp_mb()s in the lock primitives). > > Other than the lock primitives can u think of any more.
Not of the top of my head. > I verified that with llock/scond based spinlocks, those smp_mb() can be safely > removed. Good! > I didn't send that patch over yet as part of puzzle is why removing them > in EX based locks causes hackbench to jitter on quad core builds. This > required > some perf investigation but that seems to be causing some sort of livelock > with > callgraph profiling which is what I'm debugging currently :-) So there's two superfluous barriers right; the one before LOCK and the one after UNLOCK. Does removing either cause the jitter? I'm thinking that maybe its the smp_mb after UNLOCK that force flushes the store buffer that helps (MIPS has something similar). > BTW since we are on the topic we have this loop in stack unwinder which can > potentially cause RCU stalls, actual lockups etc. I was planning to add the > following - does that seem fine to you. Worries me more than anything. How could you get stuck in there? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
