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. 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? 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 do however like the idea of moving more to be protected by the lglocks, and minimizing usage of the blocked_lock_lock. -- Jeff Layton <jlayton@xxxxxxxxxxxxxxx> -- 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
