Re: [PATCH v5 5/5] drm/xe: Refactor default device atomic settings

[Nirmoy Das <nirmoy.das@intel.com>]

Hi Jose,

On 4/29/2024 3:46 PM, Souza, Jose wrote:
> On Mon, 2024-04-29 at 11:05 +0200, Nirmoy Das wrote:
>> Hi Jose,
>>
>> On 4/26/2024 11:04 PM, Souza, Jose wrote:
>>> On Fri, 2024-04-26 at 12:56 +0200, Nirmoy Das wrote:
>>>> The default behavior of device atomics depends on the
>>>> VM type and buffer allocation types. Device atomics are
>>>> expected to function with all types of allocations for
>>>> traditional applications/APIs. Additionally, in compute/SVM
>>>> API scenarios with fault mode or LR mode VMs, device atomics
>>>> must work with single-region allocations. In all other cases
>>>> device atomics should be disabled by default also on platforms
>>>> where we know device atomics doesn't on work on particular
>>>> allocations types.
>>>>
>>>> v2: Fix platform checks to correct atomics behaviour on PVC.
>>>>
>>>> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
>>>> ---
>>>>    drivers/gpu/drm/xe/xe_pt.c | 27 ++++++++++++++++++++++++---
>>>>    drivers/gpu/drm/xe/xe_vm.c |  2 +-
>>>>    2 files changed, 25 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
>>>> index 5b7930f46cf3..237e4a4985a4 100644
>>>> --- a/drivers/gpu/drm/xe/xe_pt.c
>>>> +++ b/drivers/gpu/drm/xe/xe_pt.c
>>>> @@ -619,9 +619,30 @@ xe_pt_stage_bind(struct xe_tile *tile, struct xe_vma *vma,
>>>>    	struct xe_pt *pt = xe_vma_vm(vma)->pt_root[tile->id];
>>>>    	int ret;
>>>>    
>>>> -	if ((vma->gpuva.flags & XE_VMA_ATOMIC_PTE_BIT) &&
>>>> -	    (is_devmem || !IS_DGFX(xe)))
>>>> -		xe_walk.default_pte |= XE_USM_PPGTT_PTE_AE;
>>>> +	/**
>>>> +	 * Default atomic expectations for different allocation scenarios are as follows:
>>>> +	 *
>>>> +	 * 1. Traditional API: When the VM is not in fault mode or LR mode:
>>>> +	 *    - Device atomics are expected to function with all allocations.
>>>> +	 *
>>>> +	 * 2. Compute/SVM API: When the VM is either in fault mode or LR mode:
>>>> +	 *    - Device atomics are the default behavior when the bo is placed in a single region.
>>>> +	 *    - In all other cases device atomics will be disabled with AE=0 until an application
>>>> +	 *      request differently using a ioctl like madvise.
>>>> +	 */
>>>> +	if (vma->gpuva.flags & XE_VMA_ATOMIC_PTE_BIT) {
>>>> +		if (xe_vm_in_fault_mode(xe_vma_vm(vma)) ||
>>>> +		    xe_vm_in_lr_mode(xe_vma_vm(vma))) {
>>> nit: xe_vm_in_fault_mode requires xe_vm_in_lr_mode, so you can just check for the later.
>> Will do that. I think scratch page is also part of non-traditional API,
>> I will confirm that and add that if needed.
> I think Mesa is the only driver that uses scratch patch.

In that case, enabling default atomics will be treated as in the 'else 
case'/traditional-API so will not require any change.


Thanks,

Nirmoy

>
>>
>> Thanks,
>>
>> Nirmoy
>>
>>>> +			if (bo && xe_bo_has_single_placement(bo))
>>>> +				xe_walk.default_pte |= XE_USM_PPGTT_PTE_AE;
>>>> +		} else {
>>>> +			xe_walk.default_pte |= XE_USM_PPGTT_PTE_AE;
>>>> +		}
>>>> +
>>>> +		/* Unset AE if the platform(PVC) doesn't support it */
>>>> +		if (!xe->info.has_device_atomics_on_smem && !is_devmem)
>>>> +			xe_walk.default_pte &= ~XE_USM_PPGTT_PTE_AE;
>>>> +	}
>>>>    
>>>>    	if (is_devmem) {
>>>>    		xe_walk.default_pte |= XE_PPGTT_PTE_DM;
>>>> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
>>>> index 8fc37c5a0196..f795016a80d5 100644
>>>> --- a/drivers/gpu/drm/xe/xe_vm.c
>>>> +++ b/drivers/gpu/drm/xe/xe_vm.c
>>>> @@ -805,7 +805,7 @@ static struct xe_vma *xe_vma_create(struct xe_vm *vm,
>>>>    	for_each_tile(tile, vm->xe, id)
>>>>    		vma->tile_mask |= 0x1 << id;
>>>>    
>>>> -	if (GRAPHICS_VER(vm->xe) >= 20 || vm->xe->info.platform == XE_PVC)
>>>> +	if (vm->xe->info.has_atomic_enable_pte_bit)
>>>>    		vma->gpuva.flags |= XE_VMA_ATOMIC_PTE_BIT;
>>>>    
>>>>    	vma->pat_index = pat_index;