linux-kernel - Re: [PATCH 1/3] amdkfd: Don't clear *kfd2kgd on kfd_module

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Date:	Mon, 22 Dec 2014 09:43:13 +0200
From:	Oded Gabbay <oded.gabbay@....com>
To:	Dave Airlie <airlied@...il.com>
CC:	Christian König <deathsimple@...afone.de>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"Deucher, Alexander" <Alexander.Deucher@....com>,
	"Elifaz, Dana" <Dana.Elifaz@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] amdkfd: Don't clear *kfd2kgd on kfd_module_init



On 12/22/2014 09:40 AM, Dave Airlie wrote:
>>>>>> There should be, but when the modules are compiled in, they are loaded
>>>>>> based on
>>>>>> link order only, if they are in the same group, and the groups are
>>>>>> loaded by a
>>>>>> pre-defined order.
>>>>>
>>>>> Is that really still up to date? I've seen effort to change that
>>>>> something like
>>>>> 10+ years ago when Rusty reworked the module system. And it is comming
>>>>> up on the
>>>>> lists again from time to time.
>>>>
>>>>  From what I can see in the Makefile rules, code and google, yes, that's
>>>> still
>>>> the situation. If someone will prove me wrong I will be more than happy
>>>> to
>>>> correct my code.
>>>>>
>>>>>
>>>>>> I don't want to move iommu before gpu, so I don't have a solution for
>>>>>> the
>>>>>> order between amdkfd and amd_iommu_v2.
>>>>>
>>>>> Why not? That's still better than creating a kernel workqueue,
>>>>> scheduling one
>>>>> work item on it, rescheduling the task until everything is completed and
>>>>> you can
>>>>> continue.
>>>>
>>>> Because I don't know the consequences of moving an entire subsystem in
>>>> front
>>>> of another one. In addition, even if everyone agrees, I'm pretty sure
>>>> that
>>>> Linus won't be happy to do that in -rc stages. So maybe this is something
>>>> to
>>>> consider for 3.20 merge window, but I would still like to provide a
>>>> solution
>>>> for 3.19.
>>>
>>>
>>> Yeah, true indeed. How about depending on everything being compiled as
>>> module
>>> for 3.19 then? Still better than having such a hack in the driver for as a
>>> temporary workaround for one release.
>>>
>> I thought about it, but because this problem was originally reported by a
>> user that told us he couldn't use modules because of his setup, I decided
>> not to.
>> I assume there are other users out there who needs this option (compiled
>> everything in the kernel - embedded ?), so I don't want to make their life
>> harder.
>>
>> In addition, saying it is a workaround for one release is true in case
>> moving iommu subsystem in front of gpu subsystem is acceptable and doesn't
>> cause other problems, unknown at this point.
>>
>> Bottom line, my personal preference is to help the users _now_ and if a
>> better fix is found in the future, change the code accordingly.
>
> My guess is moving the iommu subsystem in front of the GPU would be rational.
>
> It does seem like it would generally have a depend in that order.
>
> Dave.
>
Dave,
I agree, but don't you think it is too risky for -rc stages ?
If not, I can try it and if it works on KV, I can submit a patch.
But if you do think it is risky, what do you recommend for 3.19 ? Do the fix I 
suggested or disable build-in compilation option ?

	Oded
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