On 02/25/2015 02:38 AM, Ingo Molnar wrote: > * Jason Baron <jbaron@xxxxxxxxxx> wrote: > >> Hi, >> >> When we are sharing a wakeup source among multiple epoll >> fds, we end up with thundering herd wakeups, since there >> is currently no way to add to the wakeup source >> exclusively. This series introduces a new EPOLL_ROTATE >> flag to allow for round robin exclusive wakeups. >> >> I believe this patch series addresses the two main >> concerns that were raised in prior postings. Namely, that >> it affected code (and potentially performance) of the >> core kernel wakeup functions, even in cases where it was >> not strictly needed, and that it could lead to wakeup >> starvation (since we were are no longer waking up all >> waiters). It does so by adding an extra layer of >> indirection, whereby waiters are attached to a 'psuedo' >> epoll fd, which in turn is attached directly to the >> wakeup source. >> sched/wait: add __wake_up_rotate() >> include/linux/wait.h | 1 + >> kernel/sched/wait.c | 27 ++++++++++++++++++++++ > So the scheduler bits are looking good to me in principle, > because they just add a new round-robin-rotating wakeup > variant and don't disturb the others. > > Is there consensus on the epoll ABI changes? With Davide I'm not sure there is a clear consensus on this change, but I'm hoping that I've addressed the outstanding concerns in this latest version. I also think the addition of a way to do a 'wakeup policy' here will open up other 'policies', such as taking into account cpu affinity as you suggested. So, I think its potentially an interesting direction for this code. > Libenzi inactive eventpoll appears to be without a > dedicated maintainer since 2011 or so. Is there anyone who > knows the code and its usages in detail and does final ABI > decisions on eventpoll - Andrew, Al or Linus? > Generally, Andrew and Al do more 'final' reviews here, and a lot of others on lkml are always very helpful in looking at this code. However, its not always clear, at least to me, who I should pester. Thanks, -Jason -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
