Re: [PATCH] drm/xe: Opportunistically skip TLB invalidaion on unbind

["Ghimiray, Himal Prasad" <himal.prasad.ghimiray@intel.com>]

On 13-06-2025 10:06, Matthew Brost wrote:
> If a range or VMA is invalidated and scratched page is disabled, there
> is no reason to issue a TLB invalidation on unbind, skip TLB
> innvalidation is this condition is true. This is an opportunistic check
> as it is done without the notifier lock, thus it possible for the range
> or VMA to be invalidated after this check is performed.
> 
> This should improve performance of the SVM garbage collector, for
> example, xe_exec_system_allocator --r many-stride-new-prefetch, went
> ~20s to ~9.5s on a BMG.
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_pt.c  | 18 ++++++++++++++++--
>   drivers/gpu/drm/xe/xe_svm.c |  5 ++++-
>   drivers/gpu/drm/xe/xe_vm.c  |  5 ++++-
>   3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
> index f39d5cc9f411..09c3ccc81cca 100644
> --- a/drivers/gpu/drm/xe/xe_pt.c
> +++ b/drivers/gpu/drm/xe/xe_pt.c
> @@ -1988,7 +1988,14 @@ static int unbind_op_prepare(struct xe_tile *tile,
>   					 xe_vma_end(vma));
>   	++pt_update_ops->current_op;
>   	pt_update_ops->needs_userptr_lock |= xe_vma_is_userptr(vma);
> -	pt_update_ops->needs_invalidation = true;
> +
> +	/*
> +	 * Opportunistically supressing invalidation, READ_ONCE pairs with
> +	 * WRITE_ONCE in MMU notifier or BO move
> +	 */
> +	pt_update_ops->needs_invalidation |= xe_vm_has_scratch(xe_vma_vm(vma)) ||
> +		((vma->tile_present & BIT(tile->id)) &
> +		 ~READ_ONCE(vma->tile_invalidated));
>   
>   	xe_pt_commit_prepare_unbind(vma, pt_op->entries, pt_op->num_entries);
>   
> @@ -2023,7 +2030,14 @@ static int unbind_range_prepare(struct xe_vm *vm,
>   					 range->base.itree.last + 1);
>   	++pt_update_ops->current_op;
>   	pt_update_ops->needs_svm_lock = true;
> -	pt_update_ops->needs_invalidation = true;
> +
> +	/*
> +	 * Opportunistically supressing invalidation, READ_ONCE pairs with
> +	 * WRITE_ONCE in SVM MMU notifier
> +	 */
> +	pt_update_ops->needs_invalidation |= xe_vm_has_scratch(vm) ||
> +		((range->tile_present & BIT(tile->id)) &
> +		 ~READ_ONCE(range->tile_invalidated));
>   
>   	xe_pt_commit_prepare_unbind(XE_INVALID_VMA, pt_op->entries,
>   				    pt_op->num_entries);
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index 13abc6049041..5e5bf47293ad 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -141,7 +141,10 @@ xe_svm_range_notifier_event_begin(struct xe_vm *vm, struct drm_gpusvm_range *r,
>   	for_each_tile(tile, xe, id)
>   		if (xe_pt_zap_ptes_range(tile, vm, range)) {
>   			tile_mask |= BIT(id);
> -			/* Pairs with READ_ONCE in xe_svm_range_is_valid */
> +			/*
> +			 * Pairs with READ_ONCE in xe_svm_range_is_valid or PT
> +			 * code to suppress invalidation on unbind
> +			 */
>   			WRITE_ONCE(range->tile_invalidated,
>   				   range->tile_invalidated | BIT(id));
>   		}
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index d18807b92b18..b296ac37347b 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3924,7 +3924,10 @@ int xe_vm_invalidate_vma(struct xe_vma *vma)
>   	for (id = 0; id < fence_id; ++id)
>   		xe_gt_tlb_invalidation_fence_wait(&fence[id]);
>   
> -	/* WRITE_ONCE pair with READ_ONCE in xe_gt_pagefault.c */
> +	/*
> +	 * WRITE_ONCE pair with READ_ONCE in xe_gt_pagefault.c or PT code to
> +	 * suppress invalidation on unbind
> +	 */

LGTM.

Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>> 
WRITE_ONCE(vma->tile_invalidated, vma->tile_mask);
>   
>   	return ret;