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

[Bas Nieuwenhuizen]

On Fri, May 20, 2022 at 11:42 AM 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 hear you but we also have an increasing number of games that don't
even start with 3 GiB. At some point (which I'd speculate has already
been reached, I've seen a number of complaints of games that ran on
deck but not on desktop linux because on deck we set amdgpu.gttsize)
we have more games broken due to the low limit than there would be
apps broken due to a high limit.

>
> 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);
>>
>