Messages in this thread | | | Date | Thu, 14 Jul 2016 20:56:05 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] locking/percpu-rwsem: Introduce bias knob |
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On Thu, Jul 14, 2016 at 08:43:51PM +0200, Oleg Nesterov wrote: > On 07/14, Peter Zijlstra wrote: > > > > The current percpu-rwsem read side is entirely free of serializing > > instructions at the cost of having a synchronize_sched() in the write > > path. > > > > The latency of the synchronize_sched() is too high for some users > > (cgroups), so provide a __percpu_init_rwsem(.bias) argument to forgot > > this synchronize_sched() at the cost of forcing all readers into the > > slow path, which has serializing instructions. > > Oh well... I personally do not think this is what we want... Can't > we just add the stupid rcu_sync_enter() into cgroup_init() at least > for now?
> Yes, this means the unnecessary .sync() at boot time, but > it will go away after cleanups I am going to send.
Those would have to hit the same merge window though; some people (like Arjan) really care about boot times and hunt and kill people adding pointless delays..
> Because, again, we will probably want to change this bias dynamically.
Hmm, how so?
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