Re: [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging normal ones

[Peter Zijlstra]

On Wed, Jul 01, 2015 at 12:09:39PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 30, 2015 at 04:46:33PM -0700, josh@xxxxxxxxxxxxxxxx wrote:
> > Consider it a fairly weak concern against.  Increasing performance seems
> > like a good thing in general; I just don't relish the future "feels less
> > responsive" bug reports that take a long time to track down and turn out
> > to be "this completely unrelated driver was loaded and started using
> > expedited grace periods".
> 
> random drivers, or for that matter, new-code of any sort. Should _NOT_
> be using expedited grace periods.
> 
> They're a horrid hack only suitable for unfixable ABI.

Let me repeat, just in case I've not been clear. Expedited grace periods
are _BAD_ and should be avoided at all costs.

They perturb the _entire_ machine.

Yes we can polish the turd, but in the end its still a turd.

Sadly people seem to have taken a liking to them, ooh a make RCU go
faster button. And there's not been much if any pushback on people using
it.


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