Re: [PATCH 09/10] drm/amdkfd: partially actual_loc removed

[Felix Kuehling <felix.kuehling@amd.com>]

On 2021-06-21 12:04 p.m., Alex Sierra wrote:
> actual_loc should not be used anymore, as pranges
> could have mixed locations (VRAM & SYSRAM) at the
> same time.
>
> Signed-off-by: Alex Sierra <alex.sierra@amd.com>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 12 +---
>   drivers/gpu/drm/amd/amdkfd/kfd_svm.c     | 71 ++++++++++--------------
>   2 files changed, 29 insertions(+), 54 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> index f71f8d7e2b72..acb9f64577a0 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> @@ -501,12 +501,6 @@ svm_migrate_ram_to_vram(struct svm_range *prange, uint32_t best_loc,
>   	struct amdgpu_device *adev;
>   	int r = 0;
>   
> -	if (prange->actual_loc == best_loc) {
> -		pr_debug("svms 0x%p [0x%lx 0x%lx] already on best_loc 0x%x\n",
> -			 prange->svms, prange->start, prange->last, best_loc);
> -		return 0;
> -	}
> -
>   	adev = svm_range_get_adev_by_id(prange, best_loc);
>   	if (!adev) {
>   		pr_debug("failed to get device by id 0x%x\n", best_loc);
> @@ -791,11 +785,7 @@ int
>   svm_migrate_to_vram(struct svm_range *prange, uint32_t best_loc,
>   		    struct mm_struct *mm)
>   {
> -	if  (!prange->actual_loc)
> -		return svm_migrate_ram_to_vram(prange, best_loc, mm);
> -	else
> -		return svm_migrate_vram_to_vram(prange, best_loc, mm);
> -
> +	return svm_migrate_ram_to_vram(prange, best_loc, mm);

Can you remove svm_migrate_vram_to_vram in this case? I guess we're 
relying on the svm_range_prefault call in svm_migrate_ram_to_vram now to 
migrate VRAM in a different XGMI hive to system memory now. But 
eventually we want to get rid of that pre-fault hack.


>   }
>   
>   /**
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> index 3b05bc270732..ebc1ae7e5193 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> @@ -1421,42 +1421,38 @@ static int svm_range_validate_and_map(struct mm_struct *mm,
>   
>   	svm_range_reserve_bos(&ctx);
>   
> -	if (!prange->actual_loc) {
> -		p = container_of(prange->svms, struct kfd_process, svms);
> -		owner = kfd_svm_page_owner(p, find_first_bit(ctx.bitmap,
> -							MAX_GPU_INSTANCE));
> -		for_each_set_bit(idx, ctx.bitmap, MAX_GPU_INSTANCE) {
> -			if (kfd_svm_page_owner(p, idx) != owner) {
> -				owner = NULL;
> -				break;
> -			}
> -		}
> -		r = amdgpu_hmm_range_get_pages(&prange->notifier, mm, NULL,
> -					       prange->start << PAGE_SHIFT,
> -					       prange->npages, &hmm_range,
> -					       false, true, owner);
> -		if (r) {
> -			pr_debug("failed %d to get svm range pages\n", r);
> -			goto unreserve_out;
> -		}
> -
> -		r = svm_range_dma_map(prange, ctx.bitmap,
> -				      hmm_range->hmm_pfns);
> -		if (r) {
> -			pr_debug("failed %d to dma map range\n", r);
> -			goto unreserve_out;
> +	p = container_of(prange->svms, struct kfd_process, svms);
> +	owner = kfd_svm_page_owner(p, find_first_bit(ctx.bitmap,
> +						MAX_GPU_INSTANCE));
> +	for_each_set_bit(idx, ctx.bitmap, MAX_GPU_INSTANCE) {
> +		if (kfd_svm_page_owner(p, idx) != owner) {
> +			owner = NULL;
> +			break;
>   		}
> +	}
> +	r = amdgpu_hmm_range_get_pages(&prange->notifier, mm, NULL,
> +				       prange->start << PAGE_SHIFT,
> +				       prange->npages, &hmm_range,
> +				       false, true, owner);
> +	if (r) {
> +		pr_debug("failed %d to get svm range pages\n", r);
> +		goto unreserve_out;
> +	}
>   
> -		prange->validated_once = true;
> +	r = svm_range_dma_map(prange, ctx.bitmap,
> +			      hmm_range->hmm_pfns);
> +	if (r) {
> +		pr_debug("failed %d to dma map range\n", r);
> +		goto unreserve_out;
>   	}
>   
> +	prange->validated_once = true;
> +
>   	svm_range_lock(prange);
> -	if (!prange->actual_loc) {
> -		if (amdgpu_hmm_range_get_pages_done(hmm_range)) {
> -			pr_debug("hmm update the range, need validate again\n");
> -			r = -EAGAIN;
> -			goto unlock_out;
> -		}
> +	if (amdgpu_hmm_range_get_pages_done(hmm_range)) {
> +		pr_debug("hmm update the range, need validate again\n");
> +		r = -EAGAIN;
> +		goto unlock_out;

IMO, this is the most important part of this commit, and it should be 
called out the the path description. Here we use hmm_range_fault for 
getting VRAM addresses. This is what enables mixed mappings in the first 
place.

Regards,
    Felix


>   	}
>   	if (!list_empty(&prange->child_list)) {
>   		pr_debug("range split by unmap in parallel, validate again\n");
> @@ -2741,20 +2737,9 @@ svm_range_trigger_migration(struct mm_struct *mm, struct svm_range *prange,
>   	*migrated = false;
>   	best_loc = svm_range_best_prefetch_location(prange);
>   
> -	if (best_loc == KFD_IOCTL_SVM_LOCATION_UNDEFINED ||
> -	    best_loc == prange->actual_loc)
> +	if (best_loc == KFD_IOCTL_SVM_LOCATION_UNDEFINED)
>   		return 0;
>   
> -	/*
> -	 * Prefetch to GPU without host access flag, set actual_loc to gpu, then
> -	 * validate on gpu and map to gpus will be handled afterwards.
> -	 */
> -	if (best_loc && !prange->actual_loc &&
> -	    !(prange->flags & KFD_IOCTL_SVM_FLAG_HOST_ACCESS)) {
> -		prange->actual_loc = best_loc;
> -		return 0;
> -	}
> -
>   	if (!best_loc) {
>   		r = svm_migrate_vram_to_ram(prange, mm);
>   		*migrated = !r;
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