Messages in this thread |  | | Date | Wed, 18 Feb 2015 17:33:00 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v2 2/2] epoll: introduce EPOLLEXCLUSIVE and EPOLLROUNDROBIN |
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* Jason Baron <jbaron@akamai.com> wrote:
> > This has two main advantages: firstly it solves the > > O(N) (micro-)problem, but it also more evenly > > distributes events both between task-lists and within > > epoll groups as tasks as well. > > Its solving 2 issues - spurious wakeups, and more even > loading of threads. The event distribution is more even > between 'epoll groups' with this patch, however, if > multiple threads are blocking on a single 'epoll group', > this patch does not affect the the event distribution > there. [...]
Regarding your last point, are you sure about that?
If we have say 16 epoll threads registered, and if the list is static (no register/unregister activity), then the wakeup pattern is in strict order of the list: threads closer to the list head will be woken more frequently, in a wake-once fashion. So if threads do just quick work and go back to sleep quickly, then typically only the first 2-3 threads will get any runtime in practice - the wakeup iteration never gets 'deep' into the list.
With the round-robin shuffling of the list, the threads get shuffled to the tail on wakeup, which distributes events evenly: all 16 epoll threads will accumulate an even distribution of runtime, statistically.
Have I misunderstood this somehow?
Thanks,
Ingo
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