[Intel-gfx] [PATCH] intel: Delay testing for userptr until first use

[Chris Wilson]

On Tue, Nov 04, 2014 at 03:14:04PM +0000, Tvrtko Ursulin wrote:
> 
> On 11/04/2014 02:31 PM, Chris Wilson wrote:
> >Running __mmu_notifier_register() is surprisingly expensive, so let's
> >not do that unless we have to.
> 
> Affects some program startup or what? What is the cost? I would add
> some notes in the commit for future reference.

It was affecting a badly behavely igt test, that was provoking the
linear walk in mm_take_all_locks() and then causing each one to restart
due to signals... Performance fell off a cliff. This was extreme, but
one can suppose that on a similarly stressed system startup performance
will also degrade.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre