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From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] intel: Delay testing for userptr until first use
Date: Wed, 05 Nov 2014 10:07:36 +0000	[thread overview]
Message-ID: <5459F6E8.6050302@linux.intel.com> (raw)
In-Reply-To: <20141104184453.GR13658@nuc-i3427.alporthouse.com>


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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      reply	other threads:[~2014-11-05 10:07 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-11-04 14:31 [PATCH] intel: Delay testing for userptr until first use Chris Wilson
2014-11-04 14:36 ` Chris Wilson
2014-11-04 15:14 ` Tvrtko Ursulin
2014-11-04 18:44   ` Chris Wilson
2014-11-05 10:07     ` Tvrtko Ursulin [this message]

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