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

[Chen, Jiansong (Simon)]

[AMD Official Use Only]

Does't the below code in gfx_v8_ring_emit_cntxcntl do almost the same thing as dropping the preamble ib. I cannot understand why bother to duplicate the optimization and cause a mess
In the common code.
                /* set load_ce_ram if preamble presented */
                if (AMDGPU_PREAMBLE_IB_PRESENT & flags)
                        dw2 |= 0x10000000;
        } else {
                /* still load_ce_ram if this is the first time preamble presented
                 * although there is no context switch happens.
                 */
                if (AMDGPU_PREAMBLE_IB_PRESENT_FIRST & flags)
                        dw2 |= 0x10000000;
        }

-----Original Message-----
From: Christian König <ckoenig.leichtzumerken at gmail.com>
Sent: Monday, May 17, 2021 2:56 PM
To: Chen, Jiansong (Simon) <Jiansong.Chen at amd.com>; Koenig, Christian <Christian.Koenig at amd.com>; amd-gfx at lists.freedesktop.org
Subject: Re: [PATCH] drm/amdgpu: optimize to drop preamble IB for old GPUs

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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