Re: [PATCH v2 7/7] drm/xe/configfs: add disable_mem_copy knob

[Matthew Brost <matthew.brost@intel.com>]

On Mon, Oct 20, 2025 at 01:54:39PM +0100, Matthew Auld wrote:
> For easier experimentation/comparison allow turning off the newer
> MEM_COPY path, without needing to apply manual hacks and build a new
> kernel. This needs to be configured before fully probing the device.
> 
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> ---
>  drivers/gpu/drm/xe/xe_configfs.c | 65 ++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/xe/xe_configfs.h |  2 +
>  drivers/gpu/drm/xe/xe_pci.c      |  4 +-
>  3 files changed, 70 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_configfs.c b/drivers/gpu/drm/xe/xe_configfs.c
> index c1419a270fa4..df459daa0f07 100644
> --- a/drivers/gpu/drm/xe/xe_configfs.c
> +++ b/drivers/gpu/drm/xe/xe_configfs.c
> @@ -236,6 +236,15 @@
>   *
>   * This setting only takes effect when probing the device.
>   *
> + * Disable MEM_COPY path
> + * -----------------------------------------------------
> + * This config will force the use of the older XY_FAST_COPY instruction in the migration code.
> + * Intended only for experimentation.
> + *
> + *	# echo 1 > /sys/kernel/config/xe/0000:03:00.0/disable_mem_copy
> + *
> + * This setting only takes effect when probing the device.
> + *
>   * Remove devices
>   * ==============
>   *
> @@ -264,6 +273,9 @@ struct xe_config_group_device {
>  		struct {
>  			unsigned int max_vfs;
>  		} sriov;
> +		struct {
> +			bool disable_mem_copy;
> +		} migrate;
>  	} config;
>  
>  	/* protects attributes */
> @@ -282,6 +294,9 @@ static const struct xe_config_device device_defaults = {
>  	.sriov = {
>  		.max_vfs = UINT_MAX,
>  	},
> +	.migrate = {
> +		.disable_mem_copy = false,
> +	},
>  };
>  
>  static void set_device_defaults(struct xe_config_device *config)
> @@ -809,8 +824,35 @@ static ssize_t ctx_restore_post_bb_store(struct config_item *item,
>  	return wa_bb_store(dev->config.ctx_restore_post_bb, dev, data, sz);
>  }
>  
> +static ssize_t disable_mem_copy_show(struct config_item *item, char *page)
> +{
> +	struct xe_config_device *dev = to_xe_config_device(item);
> +
> +	return sprintf(page, "%d\n", dev->migrate.disable_mem_copy);
> +}
> +
> +static ssize_t disable_mem_copy_store(struct config_item *item, const char *page, size_t len)
> +{
> +	struct xe_config_group_device *dev = to_xe_config_group_device(item);
> +	bool val;
> +	int ret;
> +
> +	ret = kstrtobool(page, &val);
> +	if (ret)
> +		return ret;
> +
> +	guard(mutex)(&dev->lock);
> +	if (is_bound(dev))
> +		return -EBUSY;
> +
> +	dev->config.migrate.disable_mem_copy = val;
> +
> +	return len;
> +}
> +
>  CONFIGFS_ATTR(, ctx_restore_mid_bb);
>  CONFIGFS_ATTR(, ctx_restore_post_bb);
> +CONFIGFS_ATTR(, disable_mem_copy);
>  CONFIGFS_ATTR(, enable_psmi);
>  CONFIGFS_ATTR(, engines_allowed);
>  CONFIGFS_ATTR(, gt_types_allowed);
> @@ -819,6 +861,7 @@ CONFIGFS_ATTR(, survivability_mode);
>  static struct configfs_attribute *xe_config_device_attrs[] = {
>  	&attr_ctx_restore_mid_bb,
>  	&attr_ctx_restore_post_bb,
> +	&attr_disable_mem_copy,
>  	&attr_enable_psmi,
>  	&attr_engines_allowed,
>  	&attr_gt_types_allowed,
> @@ -1065,6 +1108,7 @@ static void dump_custom_dev_config(struct pci_dev *pdev,
>  	PRI_CUSTOM_ATTR("%llx", engines_allowed);
>  	PRI_CUSTOM_ATTR("%d", enable_psmi);
>  	PRI_CUSTOM_ATTR("%d", survivability_mode);
> +	PRI_CUSTOM_ATTR("%d", migrate.disable_mem_copy);
>  
>  #undef PRI_CUSTOM_ATTR
>  }
> @@ -1242,6 +1286,27 @@ u32 xe_configfs_get_ctx_restore_post_bb(struct pci_dev *pdev,
>  	return len;
>  }
>  
> +/**
> + * xe_configfs_migrate_disable_mem_copy - get configfs disable_mem_copy setting
> + * @pdev: pci device
> + *
> + * Return: True if fast_copy_xy instruction in migration code should be used as the default. False
> + * otherwise.
> + */
> +bool xe_configfs_migrate_disable_mem_copy(struct pci_dev *pdev)
> +{
> +	struct xe_config_group_device *dev = find_xe_config_group_device(pdev);
> +	bool disable_mem_copy;
> +
> +	if (!dev)
> +		return false;
> +
> +	disable_mem_copy = dev->config.migrate.disable_mem_copy;
> +	config_group_put(&dev->group);
> +
> +	return disable_mem_copy;
> +}
> +
>  #ifdef CONFIG_PCI_IOV
>  /**
>   * xe_configfs_get_max_vfs() - Get number of VFs that could be managed
> diff --git a/drivers/gpu/drm/xe/xe_configfs.h b/drivers/gpu/drm/xe/xe_configfs.h
> index fed57be0b90e..01f285ce56f2 100644
> --- a/drivers/gpu/drm/xe/xe_configfs.h
> +++ b/drivers/gpu/drm/xe/xe_configfs.h
> @@ -25,6 +25,7 @@ u32 xe_configfs_get_ctx_restore_mid_bb(struct pci_dev *pdev, enum xe_engine_clas
>  				       const u32 **cs);
>  u32 xe_configfs_get_ctx_restore_post_bb(struct pci_dev *pdev, enum xe_engine_class,
>  					const u32 **cs);
> +bool xe_configfs_migrate_disable_mem_copy(struct pci_dev *pdev);
>  #ifdef CONFIG_PCI_IOV
>  unsigned int xe_configfs_get_max_vfs(struct pci_dev *pdev);
>  #endif
> @@ -42,6 +43,7 @@ static inline u32 xe_configfs_get_ctx_restore_mid_bb(struct pci_dev *pdev, enum
>  static inline u32 xe_configfs_get_ctx_restore_post_bb(struct pci_dev *pdev, enum xe_engine_class,
>  						      const u32 **cs) { return 0; }
>  static inline unsigned int xe_configfs_get_max_vfs(struct pci_dev *pdev) { return UINT_MAX; }
> +bool xe_configfs_migrate_disable_mem_copy(struct pci_dev *pdev) { return false; }
>  #endif
>  
>  #endif
> diff --git a/drivers/gpu/drm/xe/xe_pci.c b/drivers/gpu/drm/xe/xe_pci.c
> index 8458d4ae8ee7..9f8a2a298216 100644
> --- a/drivers/gpu/drm/xe/xe_pci.c
> +++ b/drivers/gpu/drm/xe/xe_pci.c
> @@ -660,7 +660,9 @@ static int xe_info_init_early(struct xe_device *xe,
>  	xe->info.has_pxp = desc->has_pxp;
>  	xe->info.has_sriov = xe_configfs_primary_gt_allowed(to_pci_dev(xe->drm.dev)) &&
>  		desc->has_sriov;
> -	xe->info.has_mem_copy_instr = desc->has_mem_copy_instr;
> +	xe->info.has_mem_copy_instr =
> +		desc->has_mem_copy_instr &&
> +		!xe_configfs_migrate_disable_mem_copy(to_pci_dev(xe->drm.dev));
>  	xe->info.skip_guc_pc = desc->skip_guc_pc;
>  	xe->info.skip_mtcfg = desc->skip_mtcfg;
>  	xe->info.skip_pcode = desc->skip_pcode;
> -- 
> 2.51.0
>