Re: [PATCH v7 2/7] drm/xe/debugfs: add page-size allocation mode knob

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

On 14-07-2026 16:25, Himal Prasad Ghimiray wrote:
> From: Nareshkumar Gollakoti <naresh.kumar.g@intel.com>
> 
> Expose a debugfs control to override the page-size allocation mode used
> for user BOs.
> 
> The interface allows switching between the default allocation policy,
> forced 2M, forced 1G, and mixed allocation modes at runtime. This
> provides a simple way to validate behavior and debug page-size-dependent
> allocation flows.
> 
> The debugfs entry is built only when CONFIG_DRM_XE_DEBUG_PAGE_SIZE is
> enabled.
> 
> v2
> - update changelog to match mutex-based cur_index handling
> - reset cur_index when switching to mixed mode (sashiko)
> 
> v3
> - add CONFIG guard for page-size allocation debugfs support (Himal)
> - create debugfs entry under CONFIG_DRM_XE_DEBUG_PAGE_SIZE
> 
> v4
> - reorderd this patch with kconfig patch to ensure patch builds
> - Gurding this debug knob for only discrete graphics
> 
> v5(Himal)
> - Guard all page size calls with CONFIG_DRM_XE_DEBUG_PAGE_SIZE
> 
> Signed-off-by: Nareshkumar Gollakoti <naresh.kumar.g@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_debugfs.c | 62 +++++++++++++++++++++++++++++++++
>   1 file changed, 62 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_debugfs.c b/drivers/gpu/drm/xe/xe_debugfs.c
> index 8c391c7b017a..dcc01336538d 100644
> --- a/drivers/gpu/drm/xe/xe_debugfs.c
> +++ b/drivers/gpu/drm/xe/xe_debugfs.c
> @@ -564,6 +564,56 @@ static const struct file_operations disable_late_binding_fops = {
>   	.write = disable_late_binding_set,
>   };
>   
> +#ifdef CONFIG_DRM_XE_DEBUG_PAGE_SIZE
> +static ssize_t page_size_alloc_mode_show(struct file *f, char __user *ubuf,
> +					 size_t size, loff_t *pos)
> +{
> +	struct xe_device *xe = file_inode(f)->i_private;
> +	char buf[32];
> +	int len;
> +
> +	mutex_lock(&xe->page_size_alloc_ctrl.lock);
> +
> +	len = scnprintf(buf, sizeof(buf), "%u\n",
> +			xe->page_size_alloc_ctrl.mode);

shouldn't READ_ONCE be enough like other caller sites reading mode ?
Dont think lock is needed here.


> +	mutex_unlock(&xe->page_size_alloc_ctrl.lock);
> +
> +	return simple_read_from_buffer(ubuf, size, pos, buf, len);
> +}
> +
> +static ssize_t page_size_alloc_mode_set(struct file *f, const char __user *ubuf,
> +					size_t size, loff_t *pos)
> +{
> +	struct xe_device *xe = file_inode(f)->i_private;
> +	unsigned int val;
> +	int ret;
> +
> +	ret = kstrtouint_from_user(ubuf, size, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val > XE_PAGE_SIZE_ALLOC_CTRL_MODE_MIXED)
> +		return -EINVAL;
> +
> +	mutex_lock(&xe->page_size_alloc_ctrl.lock);
> +
> +	if (val == XE_PAGE_SIZE_ALLOC_CTRL_MODE_MIXED)
> +		xe->page_size_alloc_ctrl.cur_index = 0;
> +
> +	xe->page_size_alloc_ctrl.mode = (enum xe_page_size_alloc_ctrl_mode)val;

WRITE_ONCE to match with READ_ONCE ?

> +
> +	mutex_unlock(&xe->page_size_alloc_ctrl.lock);
> +
> +	return size;
> +}
> +
> +static const struct file_operations page_size_alloc_mode_fops = {
> +	.owner = THIS_MODULE,
> +	.read = page_size_alloc_mode_show,
> +	.write = page_size_alloc_mode_set,
> +};
> +#endif
> +
>   void xe_debugfs_register(struct xe_device *xe)
>   {
>   	struct ttm_device *bdev = &xe->ttm;
> @@ -616,6 +666,18 @@ void xe_debugfs_register(struct xe_device *xe)
>   
>   	debugfs_create_file("disable_late_binding", 0600, root, xe,
>   			    &disable_late_binding_fops);
> +#ifdef CONFIG_DRM_XE_DEBUG_PAGE_SIZE
> +	/*
> +	 * Expose a debugfs knob to control user BO page-size allocation:
> +	 * 0 - default behavior
> +	 * 1 - force 2M page allocations
> +	 * 2 - force 1G page allocations
> +	 * 3 - mixed mode: select 4K, 64K, 2M, and 1G in round-robin order
> +	 */

if (xe_debug_page_size_supported(xe))

wont it be better to use string names instead of values for debugfs 
read/write ?
something like none, 2M_pages, 1G_pages, mixed_pages



> +	if (IS_DGFX(xe))
> +		debugfs_create_file("page_size_alloc_mode", 0600, root, xe,
> +				    &page_size_alloc_mode_fops);
> +#endif
>   
>   	/*
>   	 * Don't expose page reclaim configuration file if not supported by the