On Monday 19 October 2015 03:22 PM, Peter Zijlstra wrote: > On Mon, Oct 19, 2015 at 09:46:35AM +0000, Vineet Gupta wrote: >> > On ARC we could use the atomic EXchange to implement a user space only >> > binary >> > semaphore - these atomic ops will be small duration so it is OK to spin >> > wait for a >> > little bit. That's how the old pthread library worked for ARC w/o any >> > atomic support. > That has the obvious problem of lock-holder-preemption and the horrible > performance issues that result from that. > > I think the syscall at least has deterministic behaviour, whereas that > userspace spin loop has this abysmal worst case thing.
I agree - we can add that syscall trivially and use it based on build time feature detection for atomics ! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/