[PATCH] drm/amdgpu: don't limit gtt size on apus
Christian König
christian.koenig at amd.com
Wed Jan 6 12:54:25 UTC 2021
Am 06.01.21 um 13:47 schrieb Joshua Ashton:
>
>
> On 1/6/21 7:52 AM, Christian König wrote:
>> Am 05.01.21 um 23:31 schrieb Joshua Ashton:
>>> On 1/5/21 10:10 PM, Alex Deucher wrote:
>>>> On Tue, Jan 5, 2021 at 5:05 PM Joshua Ashton <joshua at froggi.es> wrote:
>>>>>
>>>>> Since commit 24562523688b ("Revert "drm/amd/amdgpu: set gtt size
>>>>> according to system memory size only""), the GTT size was limited by
>>>>> 3GiB or VRAM size.
>>>>
>>>> The commit in question was to fix a hang with certain tests on APUs.
>>>> That should be tested again before we re-enable this. If it is fixed,
>>>> we should just revert the revert rather than special case dGPUs.
>>>>
>>>> Alex
>>>>
>>>
>>> I think the commit before the revert (ba851eed895c) has some
>>> fundamental problems:
>>>
>>> It was always specifying max(3GiB, 3/4ths RAM) of GTT, even if that
>>> wouldn't fit into say, 1GiB or 2GiB of available RAM.
>>>
>>> Limiting GTT to min(max(3GiB, VRAM), 3/4ths RAM) size on dGPUs makes
>>> sense also and is a sensible limit to avoid silly situations with
>>> overallocation and potential OOM.
>>>
>>> This patch solves both of those issues.
>>
>> No, Alex is right this approach was already tried and it causes
>> problems.
>>
>> Additional to that why should this be an issue? Even when VRAM is
>> very small on APUs we still use 3GiB of GTT.
>>
>> Regards,
>> Christian.
>
> The problem is that 3GiB of GTT isn't enough for most modern games.
You seem to misunderstand what the GTT size means here. This is the
amount of memory an application can lock down in a single command
submissions.
It is still possible for the game to use all of system memory for
textures etc... it can just happen that some buffers are temporary
marked as inaccessible for the GPU.
> My laptop has a 128MiB carveout which is not possible to be configured
> in the BIOS so I am stuck with that size without extra kernel
> parameters which shouldn't be necessary.
Did you ran into problems without the parameter?
>
> If you dislike the approach of keeping the extra check for dGPUs and
> limiting GTT there, then I would say that we should use
> gtt_size = 3/4ths system memory
> for all devices instead of
> gtt_size = max(3/4ths system memory, 3GiB)
> as it was before the revert, as it is problematic on systems with <
> 3GiB of system memory.
Yeah, that's indeed not a good idea.
Regards,
Christian.
>
> - Joshie 🐸✨
>
>>
>>>
>>> - Joshie 🐸✨
>>>
>>>>
>>>>>
>>>>> This is problematic on APUs, especially with a small carveout
>>>>> which can be as low as a fixed 128MiB, as there would be very a
>>>>> limited
>>>>> 3GiB available for video memory.
>>>>> This obviously does not meet the demands of modern applications.
>>>>>
>>>>> This patch makes it so the GTT size heuristic always uses 3/4ths of
>>>>> the system memory size on APUs (limiting the size by 3GiB/VRAM size
>>>>> only on devices with dedicated video memory).
>>>>>
>>>>> Fixes: 24562523688b ("Revert drm/amd/amdgpu: set gtt size
>>>>> according to
>>>>> system memory size only")
>>>>>
>>>>> Signed-off-by: Joshua Ashton <joshua at froggi.es>
>>>>> ---
>>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 5 +++--
>>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 12 +++++++++---
>>>>> 2 files changed, 12 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>> index 72efd579ec5e..a5a41e9272d6 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>> @@ -192,8 +192,9 @@ module_param_named(gartsize, amdgpu_gart_size,
>>>>> uint, 0600);
>>>>>
>>>>> /**
>>>>> * DOC: gttsize (int)
>>>>> - * Restrict the size of GTT domain in MiB for testing. The
>>>>> default is -1 (It's VRAM size if 3GB < VRAM < 3/4 RAM,
>>>>> - * otherwise 3/4 RAM size).
>>>>> + * Restrict the size of GTT domain in MiB for testing. The
>>>>> default is -1 (On APUs this is 3/4th
>>>>> + * of the system memory; on dGPUs this is 3GiB or VRAM sized,
>>>>> whichever is bigger,
>>>>> + * with an upper bound of 3/4th of system memory.
>>>>> */
>>>>> MODULE_PARM_DESC(gttsize, "Size of the GTT domain in megabytes
>>>>> (-1 = auto)");
>>>>> module_param_named(gttsize, amdgpu_gtt_size, int, 0600);
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>>> index 4d8f19ab1014..294f26f4f310 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>>> @@ -1865,9 +1865,15 @@ 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->gmc.mc_vram_size),
>>>>> - ((uint64_t)si.totalram *
>>>>> si.mem_unit * 3/4));
>>>>> + gtt_size = (uint64_t)si.totalram * si.mem_unit * 3/4;
>>>>> + /* If we have dedicated memory, limit our GTT size to
>>>>> + * 3GiB or VRAM size, whichever is bigger
>>>>> + */
>>>>> + if (!(adev->flags & AMD_IS_APU)) {
>>>>> + gtt_size =
>>>>> min(max(AMDGPU_DEFAULT_GTT_SIZE_MB << 20,
>>>>> + adev->gmc.mc_vram_size),
>>>>> + gtt_size);
>>>>> + }
>>>>> }
>>>>> else
>>>>> gtt_size = (uint64_t)amdgpu_gtt_size << 20;
>>>>> --
>>>>> 2.30.0
>>>>>
>>>>> _______________________________________________
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>>
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