Messages in this thread | | | Date | Wed, 24 Jun 2015 17:01:51 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 12/13] stop_machine: Remove lglock |
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On Wed, Jun 24, 2015 at 07:50:42AM -0700, Paul E. McKenney wrote: > On Wed, Jun 24, 2015 at 09:35:03AM +0200, Peter Zijlstra wrote:
> > I still don't see a problem here though; the stop_one_cpu() invocation > > for the CPU that's suffering its preemption latency will take longer, > > but so what? > > > > How does polling and dropping back to sync_rcu() generate better > > behaviour than simply waiting for the completion? > > Because if there is too much delay, synchronize_rcu() is no slower > than is synchronize_rcu_expedited(), plus synchronize_rcu() is much > more efficient.
Still confused.. How is polling and then blocking more efficient than just blocking in the first place? I'm seeing the polling as a waste of cpu time.
The thing is, if we're stalled on a stop_one_cpu() call, the sync_rcu() is equally stalled. The sync_rcu() cannot wait more efficient than we're already waiting either.
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