[PATCH] drm/amdgpu: Adjust logic around GTT size

[Marek Olšák]

1. So make gtt = ram/2. There's your 50%.

2. Not our problem.

Marek

On Fri., May 20, 2022, 05:42 Christian König, <
ckoenig.leichtzumerken at gmail.com> wrote:

> In theory we should allow much more than that. The problem is just that we
> can't.
>
> We have the following issues:
> 1. For swapping out stuff we need to make sure that we can allocate
> temporary pages.
>     Because of this TTM has a fixed 50% limit where it starts to unmap
> memory from GPUs.
>     So currently even with a higher GTT limit you can't actually use this.
>
> 2. Apart from the test case of allocating textures with increasing power
> of two until it fails we also have a bunch of extremely stupid applications.
>     E.g. stuff like looking at the amount of memory available and trying
> preallocate everything.
>
> I'm working on this for years, but there aren't easy solutions to those
> issues. Felix has opted out for adding a separate domain for KFD
> allocations, but sooner or later we need to find a solution which works for
> everybody.
>
> Christian.
>
> Am 20.05.22 um 11:14 schrieb Marek Olšák:
>
> Ignore the silly tests. We only need to make sure games work. The current
> minimum requirement for running modern games is 8GB of GPU memory. Soon it
> will be 12GB. APUs will need to support that.
>
> Marek
>
> On Fri., May 20, 2022, 03:52 Christian König, <
> ckoenig.leichtzumerken at gmail.com> wrote:
>
>> Am 19.05.22 um 16:34 schrieb Alex Deucher:
>> > The current somewhat strange logic is in place because certain
>> > GL unit tests for large textures can cause problems with the
>> > OOM killer since there is no way to link this memory to a
>> > process.  The problem is this limit is often too low for many
>> > modern games on systems with more memory so limit the logic to
>> > systems with less than 8GB of main memory.  For systems with 8
>> > or more GB of system memory, set the GTT size to 3/4 of system
>> > memory.
>>
>> It's unfortunately not only the unit tests, but some games as well.
>>
>> 3/4 of total system memory sounds reasonable to be, but I'm 100% sure
>> that this will break some tests.
>>
>> Christian.
>>
>> >
>> > Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
>> > ---
>> >   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 25 ++++++++++++++++++++-----
>> >   1 file changed, 20 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> > index 4b9ee6e27f74..daa0babcf869 100644
>> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> > @@ -1801,15 +1801,30 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
>> >       /* Compute GTT size, either bsaed on 3/4th the size of RAM size
>> >        * or whatever the user passed on module init */
>> >       if (amdgpu_gtt_size == -1) {
>> > +             const u64 eight_GB = 8192ULL * 1024 * 1024;
>> >               struct sysinfo si;
>> > +             u64 total_memory, default_gtt_size;
>> >
>> >               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));
>> > -     }
>> > -     else
>> > +             total_memory = (u64)si.totalram * si.mem_unit;
>> > +             default_gtt_size = total_memory * 3 / 4;
>> > +             /* This somewhat strange logic is in place because
>> certain GL unit
>> > +              * tests for large textures can cause problems with the
>> OOM killer
>> > +              * since there is no way to link this memory to a process.
>> > +              * The problem is this limit is often too low for many
>> modern games
>> > +              * on systems with more memory so limit the logic to
>> systems with
>> > +              * less than 8GB of main memory.
>> > +              */
>> > +             if (total_memory < eight_GB) {
>> > +                     gtt_size = min(max((AMDGPU_DEFAULT_GTT_SIZE_MB <<
>> 20),
>> > +                                        adev->gmc.mc_vram_size),
>> > +                                    default_gtt_size);
>> > +             } else {
>> > +                     gtt_size = default_gtt_size;
>> > +             }
>> > +     } else {
>> >               gtt_size = (uint64_t)amdgpu_gtt_size << 20;
>> > +     }
>> >
>> >       /* Initialize GTT memory pool */
>> >       r = amdgpu_gtt_mgr_init(adev, gtt_size);
>>
>>
>
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