[PATCH] drm/amdgpu: do not execute 0-sized IBs

[Koenig, Christian]

Am 03.10.2019 10:25 schrieb "Pelloux-prayer, Pierre-eric" <Pierre-eric.Pelloux-prayer at amd.com>:

On 03/10/2019 10:09, Christian König wrote:
> Am 03.10.19 um 10:03 schrieb Pelloux-prayer, Pierre-eric:
>> This can be safely skipped entirely.
>> This seems to help with https://bugs.freedesktop.org/show_bug.cgi?id=111481.
>
> NAK, please instead fix gmc_v10_0_flush_gpu_tlb to include at least some NOP in the submitted IBs.

Is there any interest in executing an empty (or only filled with NOPs) IB?

Yeah, we used to have some dummy zero sized IBs for the MM engines which otherwise couldn't execute a fence command.

It shouldn't matter for modern firmware/hardware, but you could actually silently break somewhere else with this, so better not do this.

Sorry should have mentioned that directly,
Christian.


Anyway I can modify the patch to do this.

Thanks,
Pierre-Eric

>
> Christian.
>
>>
>> Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
>> index 60655834d649..aa163e679f1f 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
>> @@ -227,6 +227,11 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring, unsigned num_ibs,
>>               !amdgpu_sriov_vf(adev)) /* for SRIOV preemption, Preamble CE ib must be inserted anyway */
>>               continue;
>>   +        if (ib->length_dw == 0) {
>> +            /* On Navi gmc_v10_0_flush_gpu_tlb emits 0 sized IB */
>> +            continue;
>> +        }
>> +
>>           amdgpu_ring_emit_ib(ring, job, ib, status);
>>           status &= ~AMDGPU_HAVE_CTX_SWITCH;
>>       }
>

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