[PATCH v3 2/2] drm/xe: Opportunistically skip TLB invalidaion on unbind

[Ghimiray, Himal Prasad]

On 16-06-2025 12:00, Matthew Brost wrote:
> If a range or VMA is invalidated and scratch 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
> 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.
> 
> v2:
>   - Use helper for valid check (Thomas)
> v3:
>   - Avoid skipping TLB invalidation if PTEs are removed at a higher
>     level than the range
>   - Never skip TLB invalidations for VMA
>   - Drop Himal's RB
> 
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> ---
>   drivers/gpu/drm/xe/xe_pt.c | 31 ++++++++++++++++++++++++++++++-
>   1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
> index 9c30111e8786..b6df8995e8c1 100644
> --- a/drivers/gpu/drm/xe/xe_pt.c
> +++ b/drivers/gpu/drm/xe/xe_pt.c
> @@ -1995,6 +1995,32 @@ static int unbind_op_prepare(struct xe_tile *tile,
>   	return 0;
>   }
>   
> +static bool
> +xe_pt_op_check_range_skip_invalidation(struct xe_vm_pgtable_update_op *pt_op,
> +				       struct xe_svm_range *range)
> +{
> +	struct xe_vm_pgtable_update *update = pt_op->entries;
> +
> +	XE_WARN_ON(!pt_op->num_entries);
> +
> +	/*
> +	 * We can't skip the invalidation if we are removing PTEs that span more
> +	 * than the range, do some checks to ensure we are removing PTEs that
> +	 * are invalid.
> +	 */
> +
> +	if (pt_op->num_entries > 1)
> +		return false;
> +
> +	if (update->pt->level == 0)
> +		return true;
> +
> +	if (update->pt->level == 1)
> +		return xe_svm_range_size(range) >= SZ_2M;

 >= or == ? Dont think ranges can be greater than 2 MiB.

> +
> +	return false;
> +}
> +
>   static int unbind_range_prepare(struct xe_vm *vm,
>   				struct xe_tile *tile,
>   				struct xe_vm_pgtable_update_ops *pt_update_ops,
> @@ -2023,7 +2049,10 @@ 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;
> +	pt_update_ops->needs_invalidation |= xe_vm_has_scratch(vm) ||
> +		xe_vm_has_valid_gpu_mapping(tile, range->tile_present,
> +					    range->tile_invalidated) ||
> +		!xe_pt_op_check_range_skip_invalidation(pt_op, range);
>   
>   	xe_pt_commit_prepare_unbind(XE_INVALID_VMA, pt_op->entries,
>   				    pt_op->num_entries);