Re: [PATCH v4 05/12] drm/xe: Add num_pf_work modparam

[Maciej Patelczyk <maciej.patelczyk@intel.com>]

On 26/02/2026 05:28, Matthew Brost wrote:

> Add a module parameter to control the number of page-fault work threads,
> making it easy to experiment with how different numbers of work threads
> impact performance.
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_defaults.h     |  1 +
>   drivers/gpu/drm/xe/xe_device.c       | 17 ++++++++++++++---
>   drivers/gpu/drm/xe/xe_device_types.h | 11 ++++-------
>   drivers/gpu/drm/xe/xe_module.c       |  4 ++++
>   drivers/gpu/drm/xe/xe_module.h       |  1 +
>   drivers/gpu/drm/xe/xe_pagefault.c    |  6 +++---
>   drivers/gpu/drm/xe/xe_vm.c           |  3 ++-
>   7 files changed, 29 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_defaults.h b/drivers/gpu/drm/xe/xe_defaults.h
> index 5d5d41d067c5..2e615cf896b2 100644
> --- a/drivers/gpu/drm/xe/xe_defaults.h
> +++ b/drivers/gpu/drm/xe/xe_defaults.h
> @@ -22,5 +22,6 @@
>   #define XE_DEFAULT_WEDGED_MODE			XE_WEDGED_MODE_UPON_CRITICAL_ERROR
>   #define XE_DEFAULT_WEDGED_MODE_STR		"upon-critical-error"
>   #define XE_DEFAULT_SVM_NOTIFIER_SIZE		512
> +#define XE_DEFAULT_NUM_PF_WORK			2
>   
>   #endif
> diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
> index 3462645ca13c..0571079a09e8 100644
> --- a/drivers/gpu/drm/xe/xe_device.c
> +++ b/drivers/gpu/drm/xe/xe_device.c
> @@ -436,6 +436,18 @@ static void xe_device_destroy(struct drm_device *dev, void *dummy)
>   	ttm_device_fini(&xe->ttm);
>   }
>   
> +static void xe_device_parse_modparam(struct xe_device *xe)
> +{
> +	xe->info.force_execlist = xe_modparam.force_execlist;
> +	xe->atomic_svm_timeslice_ms = 5;
> +	xe->min_run_period_lr_ms = 5;
> +	xe->info.num_pf_work = xe_modparam.num_pf_work;
> +	if (xe->info.num_pf_work < 1)
> +		xe->info.num_pf_work = 1;
> +	else if (xe->info.num_pf_work > XE_PAGEFAULT_WORK_MAX)
> +		xe->info.num_pf_work = XE_PAGEFAULT_WORK_MAX;
> +}
> +
>   struct xe_device *xe_device_create(struct pci_dev *pdev,
>   				   const struct pci_device_id *ent)
>   {
> @@ -469,9 +481,8 @@ struct xe_device *xe_device_create(struct pci_dev *pdev,
>   
>   	xe->info.devid = pdev->device;
>   	xe->info.revid = pdev->revision;
> -	xe->info.force_execlist = xe_modparam.force_execlist;
> -	xe->atomic_svm_timeslice_ms = 5;
> -	xe->min_run_period_lr_ms = 5;
> +
> +	xe_device_parse_modparam(xe);
>   
>   	err = xe_irq_init(xe);
>   	if (err)
> diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
> index 0558dfd52541..a027ca5f6828 100644
> --- a/drivers/gpu/drm/xe/xe_device_types.h
> +++ b/drivers/gpu/drm/xe/xe_device_types.h
> @@ -130,6 +130,8 @@ struct xe_device {
>   		u8 revid;
>   		/** @info.step: stepping information for each IP */
>   		struct xe_step_info step;
> +		/** @info.num_pf_work: Number of page fault work thread */
> +		int num_pf_work;
>   		/** @info.dma_mask_size: DMA address bits */
>   		u8 dma_mask_size;
>   		/** @info.vram_flags: Vram flags */
> @@ -310,14 +312,9 @@ struct xe_device {
>   		struct rw_semaphore lock;
>   		/** @usm.pf_wq: page fault work queue, unbound, high priority */
>   		struct workqueue_struct *pf_wq;
> -		/*
> -		 * We pick 4 here because, in the current implementation, it
> -		 * yields the best bandwidth utilization of the kernel paging
> -		 * engine.
> -		 */
> -#define XE_PAGEFAULT_WORK_COUNT	4
> +#define XE_PAGEFAULT_WORK_MAX	8
>   		/** @usm.pf_workers: Page fault workers */
> -		struct xe_pagefault_work pf_workers[XE_PAGEFAULT_WORK_COUNT];
> +		struct xe_pagefault_work pf_workers[XE_PAGEFAULT_WORK_MAX];
>   		/** @usm.pf_queue: Page fault queue */
>   		struct xe_pagefault_queue pf_queue;
>   #if IS_ENABLED(CONFIG_DRM_XE_PAGEMAP)
> diff --git a/drivers/gpu/drm/xe/xe_module.c b/drivers/gpu/drm/xe/xe_module.c
> index 903d3b433421..c750db4b579c 100644
> --- a/drivers/gpu/drm/xe/xe_module.c
> +++ b/drivers/gpu/drm/xe/xe_module.c
> @@ -28,6 +28,7 @@ struct xe_modparam xe_modparam = {
>   	.max_vfs =		XE_DEFAULT_MAX_VFS,
>   #endif
>   	.wedged_mode =		XE_DEFAULT_WEDGED_MODE,
> +	.num_pf_work =		XE_DEFAULT_NUM_PF_WORK,
>   	.svm_notifier_size =	XE_DEFAULT_SVM_NOTIFIER_SIZE,
>   	/* the rest are 0 by default */
>   };
> @@ -81,6 +82,9 @@ MODULE_PARM_DESC(wedged_mode,
>   		 "Module's default policy for the wedged mode (0=never, 1=upon-critical-error, 2=upon-any-hang-no-reset "
>   		 "[default=" XE_DEFAULT_WEDGED_MODE_STR "])");
>   
> +module_param_named(num_pf_work, xe_modparam.num_pf_work, int, 0600);
> +MODULE_PARM_DESC(num_pf_work, "Number of page fault work threads, default=2, min=1, max=8");
> +
>   static int xe_check_nomodeset(void)
>   {
>   	if (drm_firmware_drivers_only())
> diff --git a/drivers/gpu/drm/xe/xe_module.h b/drivers/gpu/drm/xe/xe_module.h
> index 79cb9639c0f3..c6642523184a 100644
> --- a/drivers/gpu/drm/xe/xe_module.h
> +++ b/drivers/gpu/drm/xe/xe_module.h
> @@ -22,6 +22,7 @@ struct xe_modparam {
>   	unsigned int max_vfs;
>   #endif
>   	unsigned int wedged_mode;
> +	unsigned int num_pf_work;
>   	u32 svm_notifier_size;
>   };
>   
> diff --git a/drivers/gpu/drm/xe/xe_pagefault.c b/drivers/gpu/drm/xe/xe_pagefault.c
> index 7880fc7e7eb4..64b1dc574ab7 100644
> --- a/drivers/gpu/drm/xe/xe_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_pagefault.c
> @@ -383,7 +383,7 @@ int xe_pagefault_init(struct xe_device *xe)
>   
>   	xe->usm.pf_wq = alloc_workqueue("xe_page_fault_work_queue",
>   					WQ_UNBOUND | WQ_HIGHPRI,
> -					XE_PAGEFAULT_WORK_COUNT);
> +					xe->info.num_pf_work);
>   	if (!xe->usm.pf_wq)
>   		return -ENOMEM;
>   
> @@ -391,7 +391,7 @@ int xe_pagefault_init(struct xe_device *xe)
>   	if (err)
>   		goto err_out;
>   
> -	for (i = 0; i < XE_PAGEFAULT_WORK_COUNT; ++i) {
> +	for (i = 0; i < xe->info.num_pf_work; ++i) {
>   		struct xe_pagefault_work *pf_work = xe->usm.pf_workers + i;
>   
>   		pf_work->xe = xe;
> @@ -457,7 +457,7 @@ static int xe_pagefault_work_index(struct xe_device *xe)
>   {
>   	lockdep_assert_held(&xe->usm.pf_queue.lock);
>   
> -	return xe->usm.current_pf_work++ % XE_PAGEFAULT_WORK_COUNT;
> +	return xe->usm.current_pf_work++ % xe->info.num_pf_work;
>   }
>   
>   /**
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 06669e9c500d..54c7d0f791e1 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3070,7 +3070,8 @@ static int prefetch_ranges(struct xe_vm *vm, struct xe_vma_ops *vops,
>   	skip_threads =  op->prefetch_range.ranges_count == 1 ||
>   		(!dpagemap && !(vops->flags &
>   				XE_VMA_OPS_FLAG_HAS_SVM_VALID_RANGE)) ||
> -		!(vops->flags & XE_VMA_OPS_FLAG_DOWNGRADE_LOCK);
> +		!(vops->flags & XE_VMA_OPS_FLAG_DOWNGRADE_LOCK) ||
> +		vm->xe->info.num_pf_work == 1;
>   	thread = skip_threads ? &stack_thread : NULL;
>   
>   	if (!skip_threads) {

In addition to patch 04, we go down with workers to 2 by default.

Good idea to have this as a modparam!

Reviewed-by: Maciej Patelczyk <maciej.patelczyk@intel.com>