[PATCH] drm/amdgpu: optimize to drop preamble IB for old GPUs

[Christian König]

Am 17.05.21 um 08:51 schrieb Chen, Jiansong (Simon):
> [AMD Official Use Only]
>
> Doesn't  current solution always enable the optimization in a safe and more clear way?

No, we also need this for gfx8 where gfxoff is currently not implemented.

Additional to that we mix common frontend handling into the backend with 
this approach.

But you could clean up the code in amdgpu_ib_schedule() quite a bit.

Regards,
Christian.

> 1. for gfx8/9/10 we use load_ce_ram in context_control to control the optimization.
> 2. for gfx6/7, we directly drop the preamble ib.
>
> Regards,
> Jiansong
> -----Original Message-----
> From: Koenig, Christian <Christian.Koenig at amd.com>
> Sent: Monday, May 17, 2021 2:42 PM
> To: Chen, Jiansong (Simon) <Jiansong.Chen at amd.com>; amd-gfx at lists.freedesktop.org
> Subject: Re: [PATCH] drm/amdgpu: optimize to drop preamble IB for old GPUs
>
> Well NAK, as discussed checking the global flag is more flexible since it will still enable the preamble drop when gfxoff is disabled.
>
> Christian.
>
> Am 17.05.21 um 06:39 schrieb Jiansong Chen:
>> The optimization is safe for old GPUs and can help performance.
>>
>> Signed-off-by: Jiansong Chen <Jiansong.Chen at amd.com>
>> Change-Id: Id3b1250f1fe46dddbe8498894fb97e9753b7cafe
>> ---
>>    drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c | 6 ++++++
>>    drivers/gpu/drm/amd/amdgpu/gfx_v7_0.c | 6 ++++++
>>    2 files changed, 12 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c
>> b/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c
>> index 3a8d52a54873..c915cc439484 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c
>> @@ -1873,6 +1873,12 @@ static void gfx_v6_0_ring_emit_ib(struct amdgpu_ring *ring,
>>                amdgpu_ring_write(ring, 0);
>>        }
>>
>> +     /* drop the CE preamble IB for the same context */
>> +     if ((ib->flags & AMDGPU_IB_FLAG_PREAMBLE) &&
>> +         !(flags & AMDGPU_HAVE_CTX_SWITCH) &&
>> +         !(flags & AMDGPU_PREAMBLE_IB_PRESENT_FIRST))
>> +             return;
>> +
>>        if (ib->flags & AMDGPU_IB_FLAG_CE)
>>                header = PACKET3(PACKET3_INDIRECT_BUFFER_CONST, 2);
>>        else
>> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v7_0.c
>> b/drivers/gpu/drm/amd/amdgpu/gfx_v7_0.c
>> index c35fdd2ef2d4..6d9ccae48024 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v7_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v7_0.c
>> @@ -2269,6 +2269,12 @@ static void gfx_v7_0_ring_emit_ib_gfx(struct amdgpu_ring *ring,
>>                amdgpu_ring_write(ring, 0);
>>        }
>>
>> +     /* drop the CE preamble IB for the same context */
>> +     if ((ib->flags & AMDGPU_IB_FLAG_PREAMBLE) &&
>> +         !(flags & AMDGPU_HAVE_CTX_SWITCH) &&
>> +         !(flags & AMDGPU_PREAMBLE_IB_PRESENT_FIRST))
>> +             return;
>> +
>>        if (ib->flags & AMDGPU_IB_FLAG_CE)
>>                header = PACKET3(PACKET3_INDIRECT_BUFFER_CONST, 2);
>>        else
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