Messages in this thread |  | | Date | Thu, 14 Jul 2016 08:08:45 -0400 | From | Tejun Heo <> | Subject | Re: Severe performance regression w/ 4.4+ on Android due to cgroup locking changes |
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On Thu, Jul 14, 2016 at 02:04:28PM +0200, Peter Zijlstra wrote: > > I think it probably makes sense to make this the default on !RT at > > least with a separate patch w/o stable cc'd. While most use cases > > will be fine with the latency on write path, it also means that the > > reader side is blocked for the duration which can hurt. rwsem implies > > a lot more readers and thus more read lock operations than writes. > > It's weird to trade off higher latency for lower cpu usage when it > > would also slow down all readers. > > NAK, no expedited muck by default. There's more than just RT that > doesn't like IPI sprays.
Can you elaborate? If that's the case, we have the wrong implemention for percpu-rwsem where very long delays for writers induce the same level of delays to all readers. If expedited by default isn't workable, we should move away from rcu_sync for percpu_rwsem.
Thanks.
-- tejun
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