Re: [PATCH] drm/amd/amdgpu: set gtt size according to system memory size only

["Christian König" <christian.koenig-5C7GfCeVMHo@public.gmane.org>]

Am 07.12.2017 um 18:34 schrieb Michel Dänzer:
> On 2017-11-29 10:12 AM, Roger He wrote:
>> Change-Id: Ib634375b90d875fe04a890fc82fb1e3b7112676a
>> Signed-off-by: Roger He <Hongbo.He@amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 8 +++-----
>>   1 file changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> index 17bf0ce..d0661907 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> @@ -1330,11 +1330,9 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
>>   		struct sysinfo si;
>>   
>>   		si_meminfo(&si);
>> -		gtt_size = min(max((AMDGPU_DEFAULT_GTT_SIZE_MB << 20),
>> -			       adev->mc.mc_vram_size),
>> -			       ((uint64_t)si.totalram * si.mem_unit * 3/4));
>> -	}
>> -	else
>> +		gtt_size = max(AMDGPU_DEFAULT_GTT_SIZE_MB << 20,
>> +			(uint64_t)si.totalram * si.mem_unit * 3/4);
>> +	} else
>>   		gtt_size = (uint64_t)amdgpu_gtt_size << 20;
>>   	r = ttm_bo_init_mm(&adev->mman.bdev, TTM_PL_TT, gtt_size >> PAGE_SHIFT);
>>   	if (r) {
>>
> I'm unable to finish a piglit run (using Mesa on Tonga in a Ryzen 7 1700
> system with 16 GB of RAM) with this change. Before, I had
>
>   [drm] amdgpu: 3072M of GTT memory ready.
>
> now it's
>
>   [drm] amdgpu: 10473M of GTT memory ready.
>
> While running piglit, there's lots of
>
>   [TTM] Out of kernel memory
>
> messages, followed by more badness, and eventually the machine becomes
> inaccessible via SSH and has to be hard rebooted.
>
>
> It occurred to me one thing not being taken into account here is that
> system memory is also needed for storing the contents of BOs evicted
> from VRAM. So I tried subtracting the VRAM size, resulting in
>
>   [drm] amdgpu: 8425M of GTT memory ready.
>
> but the problem still happened. So I tried 1/2 instead of 3/4 of RAM,
> resulting in
>
>   [drm] amdgpu: 6982M of GTT memory ready.
>
> and was able to finish a piglit run with that.

I think I know what is going on here. The max-texture-size keeps 
increasing the texture size as long as it doesn't fails to allocate one.

So the "Out of kernel memory" message is actually the desired effect 
(but we should probably remove the message).

The price question is what happens after that? Those code paths are 
probably not very well tested.

Christian.
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