On 12/13/2012 01:06 AM, Oleg Nesterov wrote: > On 12/12, Oleg Nesterov wrote: >> >> On 12/12, Srivatsa S. Bhat wrote: >>> >>> On 12/12/2012 10:47 PM, Oleg Nesterov wrote: >>>> >>>> Why it needs to be per-cpu? It can be global and __read_mostly to avoid >>>> the false-sharing. OK, perhaps to put reader_percpu_refcnt/writer_signal >>>> into a single cacheline... >>> >>> Even I realized this (that we could use a global) after posting out the >>> series.. But do you think that it would be better to retain the per-cpu >>> variant itself, due to the cache effects? >> >> I don't really know, up to you. This was the question ;) > > But perhaps there is another reason to make it per-cpu... > > It seems we can avoid cpu_hotplug.active_writer == current check in > get/put. > > take_cpu_down() can clear this_cpu(writer_signal) right after it takes > hotplug_rwlock for writing. It runs with irqs and preemption disabled, > nobody else will ever look at writer_signal on its CPU. >
Hmm.. And then the get/put_ on that CPU will increment/decrement the per-cpu refcount, but we don't care.. because we only need to ensure that they don't deadlock by taking the rwlock for read. This sounds great! Regards, Srivatsa S. Bhat -- 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/
