[PATCH] drm/xe: Fix page fault queue calculation

[Matthew Brost]

On Thu, May 01, 2025 at 06:32:20PM +0000, Stuart Summers wrote:
> We followed up with the design architects to have a more
> precise calculation for a theoretical maximum number of
> page faults we might expect based on the number of TLBs
> available in the system. Fix the original calculation which
> did not take the number of TLBs into consideration.
> 

It would be helpful if we could get this information into the bspec.

Anyways, thanks for following up here:
Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> Fixes: 29582e0ea75c ("drm/xe: Add page queue multiplier")
> Fixes: 3338e4f90c14 ("drm/xe: Use topology to determine page fault queue size")
> 
> Signed-off-by: Stuart Summers <stuart.summers at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_gt_pagefault.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_pagefault.c b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> index 10622ca471a2..80a816c3837b 100644
> --- a/drivers/gpu/drm/xe/xe_gt_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> @@ -436,15 +436,20 @@ static int xe_alloc_pf_queue(struct xe_gt *gt, struct pf_queue *pf_queue)
>  				XE_MAX_EU_FUSE_BITS) * num_dss;
>  
>  	/*
> -	 * user can issue separate page faults per EU and per CS
> +	 * Each TLB can report up to 32 faults. The number of TLBs is
> +	 * equal to the number of render/compute/media engines plus twice
> +	 * the number of copy engines plus the number of EUs.
>  	 *
> -	 * XXX: Multiplier required as compute UMD are getting PF queue errors
> -	 * without it. Follow on why this multiplier is required.
> +	 * Reserve enough space here to ensure we are able to cover that
> +	 * theoretical maximum.
>  	 */
> -#define PF_MULTIPLIER	8
> +#define MAX_FAULTS_PER_TLB	32
>  	pf_queue->num_dw =
> -		(num_eus + XE_NUM_HW_ENGINES) * PF_MSG_LEN_DW * PF_MULTIPLIER;
> -#undef PF_MULTIPLIER
> +		PF_MSG_LEN_DW * MAX_FAULTS_PER_TLB *
> +		(num_eus +
> +		 hweight64(gt->info.engine_mask) +
> +		 hweight32(xe_hw_engine_mask_per_class(gt, XE_ENGINE_CLASS_COPY)));
> +#undef MAX_FAULTS_PER_TLB
>  
>  	pf_queue->gt = gt;
>  	pf_queue->data = devm_kcalloc(xe->drm.dev, pf_queue->num_dw,
> -- 
> 2.34.1
>