On 11/04/2014 06:44 PM, Chris Wilson wrote:
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.
Oh, so restarting the ioctl based on EINTR which propagates all the way
up from mm_take_all_locks? Can't really imagine a signal torture similar
to IGT in real life but check on first use makes sense anyway.
Regards,
Tvrtko
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