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

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Message-ID: <5497E3D7.1060405@amd.com>
Date:	Mon, 22 Dec 2014 11:26:47 +0200
From:	Oded Gabbay <oded.gabbay@....com>
To:	Christian König <deathsimple@...afone.de>,
	"Dave Airlie" <airlied@...il.com>
CC:	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 10:57 AM, Christian König wrote:
> Am 22.12.2014 um 08:43 schrieb Oded Gabbay:
>>
>>
>> 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 ?
>
> I would say create the patch of changing the order (should be trivial), describe
> in detail in the commit message what this is supposed to fix and why such an
> severe change was done in -rc1 and submit it upstream.
>
> We can still revert it in -rc2 if it breaks anything.
>
> Christian.
>
>>
>>     Oded
>

OK, I'll try it on my machine and if it works, I will send the patch to the list.

	Oded
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