Sorry for the late response. Got dragged away. On 02/24/2015 10:06 PM, Jeff Layton wrote: > On Tue, 24 Feb 2015 16:58:26 +0100 > Daniel Wagner <daniel.wagner@xxxxxxxxxxxx> wrote: > >> On 02/20/2015 05:05 PM, Andi Kleen wrote: >>> Daniel Wagner <daniel.wagner@xxxxxxxxxxxx> writes: >>>> >>>> I am looking at how to get rid of lglock. Reason being -rt is not too >>>> happy with that lock, especially that it uses arch_spinlock_t and >>> >>> AFAIK it could just use normal spinlock. Have you tried that? >> >> I have tried it. At least fs/locks.c didn't blow up. The benchmark >> results (lockperf) indicated that using normal spinlocks is even >> slightly faster. Simply converting felt like cheating. It might be >> necessary for the other user (kernel/stop_machine.c). Currently it looks >> like there is some additional benefit getting lglock away in fs/locks.c. >> > > What would that benefit be? > > lglocks are basically percpu spinlocks. Fixing some underlying > infrastructure that provides that seems like it might be a better > approach than declaring them "manually" and avoiding them altogether. > > Note that you can still do basically what you're proposing here with > lglocks as well. Avoid using lg_global_* and just lock each one in > turn. Yes, that was I was referring to as benefit. My main point is that there are only lg_local_* calls we could as well use normal spinlocks. No need to fancy. > That said, now that I've thought about this, I'm not sure that's really > something we want to do when accessing /proc/locks. If you lock each > one in turn, then you aren't freezing the state of the file_lock_list > percpu lists. Won't that mean that you aren't necessarily getting a > consistent view of the locks on those lists when you cat /proc/locks? Maybe I am overlooking something here but I don't see a consistency problem. We list a blocker and all its waiter in a go since only the blocker is added to flock_lock_list and the waiters are added blocker's fl_block list. > I think having a consistent view there might trump any benefit to > performance. Reading /proc/locks is a *very* rare activity in the big > scheme of things. I agree, but I hope that I got it right with my consistency argument than there shouldn't be a problem. > I do however like the idea of moving more to be protected by the > lglocks, and minimizing usage of the blocked_lock_lock. Good to hear. I am trying to write a new test (a variation of the dinning philosophers 'problem') case which benchmarks blocked_lock_lock after the re-factoring. cheers, daniel -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
