Re: [PATCH v2 5/7] drm/xe: Wait on in-syncs when swicthing to dma-fence mode

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Fri, 2025-12-12 at 10:28 -0800, Matthew Brost wrote:
> If a dma-fence submission has in-fences and pagefault queues are
> running
> work, there is little incentive to kick the pagefault queues off the
> hardware until the dma-fence submission is ready to run. Therefore,
> wait
> on the in-fences of the dma-fence submission before removing the
> pagefault queues from the hardware.
> 
> v2:
>  - Fix kernel doc (CI)
>  - Don't wait under lock (Thomas)
>  - Make wait interruptable
> 
> Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_exec.c            |  9 +++--
>  drivers/gpu/drm/xe/xe_hw_engine_group.c | 44 +++++++++++++++++++++--
> --
>  drivers/gpu/drm/xe/xe_hw_engine_group.h |  4 ++-
>  drivers/gpu/drm/xe/xe_sync.c            | 29 ++++++++++++++++
>  drivers/gpu/drm/xe/xe_sync.h            |  2 ++
>  5 files changed, 78 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec.c
> b/drivers/gpu/drm/xe/xe_exec.c
> index 4d81210e41f5..d462add2d005 100644
> --- a/drivers/gpu/drm/xe/xe_exec.c
> +++ b/drivers/gpu/drm/xe/xe_exec.c
> @@ -121,7 +121,7 @@ int xe_exec_ioctl(struct drm_device *dev, void
> *data, struct drm_file *file)
>  	u64 addresses[XE_HW_ENGINE_MAX_INSTANCE];
>  	struct drm_gpuvm_exec vm_exec = {.extra.fn = xe_exec_fn};
>  	struct drm_exec *exec = &vm_exec.exec;
> -	u32 i, num_syncs, num_ufence = 0;
> +	u32 i, num_syncs, num_in_sync = 0, num_ufence = 0;
>  	struct xe_validation_ctx ctx;
>  	struct xe_sched_job *job;
>  	struct xe_vm *vm;
> @@ -182,6 +182,9 @@ int xe_exec_ioctl(struct drm_device *dev, void
> *data, struct drm_file *file)
>  
>  		if (xe_sync_is_ufence(&syncs[num_syncs]))
>  			num_ufence++;
> +
> +		if (!num_in_sync &&
> xe_sync_needs_wait(&syncs[num_syncs]))
> +			num_in_sync++;
>  	}
>  
>  	if (XE_IOCTL_DBG(xe, num_ufence > 1)) {
> @@ -202,7 +205,9 @@ int xe_exec_ioctl(struct drm_device *dev, void
> *data, struct drm_file *file)
>  	mode = xe_hw_engine_group_find_exec_mode(q);
>  
>  	if (mode == EXEC_MODE_DMA_FENCE) {
> -		err = xe_hw_engine_group_get_mode(group, mode,
> &previous_mode);
> +		err = xe_hw_engine_group_get_mode(group, mode,
> &previous_mode,
> +						  syncs, num_in_sync
> ?
> +						  num_syncs : 0);
>  		if (err)
>  			goto err_syncs;
>  	}
> diff --git a/drivers/gpu/drm/xe/xe_hw_engine_group.c
> b/drivers/gpu/drm/xe/xe_hw_engine_group.c
> index 4d9263a1a208..022fc0c30d38 100644
> --- a/drivers/gpu/drm/xe/xe_hw_engine_group.c
> +++ b/drivers/gpu/drm/xe/xe_hw_engine_group.c
> @@ -11,6 +11,7 @@
>  #include "xe_gt.h"
>  #include "xe_gt_stats.h"
>  #include "xe_hw_engine_group.h"
> +#include "xe_sync.h"
>  #include "xe_vm.h"
>  
>  static void
> @@ -21,7 +22,8 @@ hw_engine_group_resume_lr_jobs_func(struct
> work_struct *w)
>  	int err;
>  	enum xe_hw_engine_group_execution_mode previous_mode;
>  
> -	err = xe_hw_engine_group_get_mode(group, EXEC_MODE_LR,
> &previous_mode);
> +	err = xe_hw_engine_group_get_mode(group, EXEC_MODE_LR,
> &previous_mode,
> +					  NULL, 0);
>  	if (err)
>  		return;
>  
> @@ -189,10 +191,12 @@ void
> xe_hw_engine_group_resume_faulting_lr_jobs(struct xe_hw_engine_group
> *group
>  /**
>   * xe_hw_engine_group_suspend_faulting_lr_jobs() - Suspend the
> faulting LR jobs of this group
>   * @group: The hw engine group
> + * @has_deps: dma-fence job triggering suspend has dependencies
>   *
>   * Return: 0 on success, negative error code on error.
>   */
> -static int xe_hw_engine_group_suspend_faulting_lr_jobs(struct
> xe_hw_engine_group *group)
> +static int xe_hw_engine_group_suspend_faulting_lr_jobs(struct
> xe_hw_engine_group *group,
> +						       bool
> has_deps)
>  {
>  	int err;
>  	struct xe_exec_queue *q;
> @@ -201,11 +205,19 @@ static int
> xe_hw_engine_group_suspend_faulting_lr_jobs(struct xe_hw_engine_group
>  	lockdep_assert_held_write(&group->mode_sem);
>  
>  	list_for_each_entry(q, &group->exec_queue_list,
> hw_engine_group_link) {
> +		bool idle_skip_suspend;
> +
>  		if (!xe_vm_in_fault_mode(q->vm))
>  			continue;
>  
> +		idle_skip_suspend =
> xe_exec_queue_idle_skip_suspend(q);
> +		if (!idle_skip_suspend && has_deps)
> +			return -EAGAIN;
> +
>  		xe_gt_stats_incr(q->gt,
> XE_GT_STATS_ID_HW_ENGINE_GROUP_SUSPEND_LR_QUEUE_COUNT, 1);
> -		need_resume |= !xe_exec_queue_idle_skip_suspend(q);
> +
> +
> +		need_resume |= !idle_skip_suspend;
>  		q->ops->suspend(q);
>  	}
>  
> @@ -258,7 +270,7 @@ static int
> xe_hw_engine_group_wait_for_dma_fence_jobs(struct xe_hw_engine_group
>  	return 0;
>  }
>  
> -static int switch_mode(struct xe_hw_engine_group *group)
> +static int switch_mode(struct xe_hw_engine_group *group, bool
> has_deps)
>  {
>  	int err = 0;
>  	enum xe_hw_engine_group_execution_mode new_mode;
> @@ -268,7 +280,8 @@ static int switch_mode(struct xe_hw_engine_group
> *group)
>  	switch (group->cur_mode) {
>  	case EXEC_MODE_LR:
>  		new_mode = EXEC_MODE_DMA_FENCE;
> -		err =
> xe_hw_engine_group_suspend_faulting_lr_jobs(group);
> +		err =
> xe_hw_engine_group_suspend_faulting_lr_jobs(group,
> +								 
> has_deps);
>  		break;
>  	case EXEC_MODE_DMA_FENCE:
>  		new_mode = EXEC_MODE_LR;
> @@ -289,14 +302,18 @@ static int switch_mode(struct
> xe_hw_engine_group *group)
>   * @group: The hw engine group
>   * @new_mode: The new execution mode
>   * @previous_mode: Pointer to the previous mode provided for use by
> caller
> + * @syncs: Syncs from exec IOCTL
> + * @num_syncs: Number of syncs from exec IOCTL
>   *
>   * Return: 0 if successful, -EINTR if locking failed.
>   */
>  int xe_hw_engine_group_get_mode(struct xe_hw_engine_group *group,
>  				enum
> xe_hw_engine_group_execution_mode new_mode,
> -				enum
> xe_hw_engine_group_execution_mode *previous_mode)
> +				enum
> xe_hw_engine_group_execution_mode *previous_mode,
> +				struct xe_sync_entry *syncs, int
> num_syncs)
>  __acquires(&group->mode_sem)
>  {
> +	bool has_deps = !!num_syncs;
>  	int err = down_read_interruptible(&group->mode_sem);
>  
>  	if (err)
> @@ -306,14 +323,27 @@ __acquires(&group->mode_sem)
>  
>  	if (new_mode != group->cur_mode) {
>  		up_read(&group->mode_sem);
> +retry:
>  		err = down_write_killable(&group->mode_sem);
>  		if (err)
>  			return err;
>  
>  		if (new_mode != group->cur_mode) {
> -			err = switch_mode(group);
> +			err = switch_mode(group, has_deps);
>  			if (err) {
>  				up_write(&group->mode_sem);
> +				if (err == -EAGAIN) {
> +					int i;
> +
> +					for (i = 0; i < num_syncs;
> ++i) {
> +						err =
> xe_sync_entry_wait(syncs + i);
> +						if (err)
> +							return err;
> +					}
> +
> +					has_deps = false;
> +					goto retry;
> +				}
>  				return err;
>  			}
>  		}
> diff --git a/drivers/gpu/drm/xe/xe_hw_engine_group.h
> b/drivers/gpu/drm/xe/xe_hw_engine_group.h
> index 797ee81acbf2..8b17ccd30b70 100644
> --- a/drivers/gpu/drm/xe/xe_hw_engine_group.h
> +++ b/drivers/gpu/drm/xe/xe_hw_engine_group.h
> @@ -11,6 +11,7 @@
>  struct drm_device;
>  struct xe_exec_queue;
>  struct xe_gt;
> +struct xe_sync_entry;
>  
>  int xe_hw_engine_setup_groups(struct xe_gt *gt);
>  
> @@ -19,7 +20,8 @@ void xe_hw_engine_group_del_exec_queue(struct
> xe_hw_engine_group *group, struct
>  
>  int xe_hw_engine_group_get_mode(struct xe_hw_engine_group *group,
>  				enum
> xe_hw_engine_group_execution_mode new_mode,
> -				enum
> xe_hw_engine_group_execution_mode *previous_mode);
> +				enum
> xe_hw_engine_group_execution_mode *previous_mode,
> +				struct xe_sync_entry *syncs, int
> num_syncs);
>  void xe_hw_engine_group_put(struct xe_hw_engine_group *group);
>  
>  enum xe_hw_engine_group_execution_mode
> diff --git a/drivers/gpu/drm/xe/xe_sync.c
> b/drivers/gpu/drm/xe/xe_sync.c
> index 1fc4fa278b78..d970e11962ff 100644
> --- a/drivers/gpu/drm/xe/xe_sync.c
> +++ b/drivers/gpu/drm/xe/xe_sync.c
> @@ -228,6 +228,35 @@ int xe_sync_entry_add_deps(struct xe_sync_entry
> *sync, struct xe_sched_job *job)
>  	return 0;
>  }
>  
> +/**
> + * xe_sync_entry_wait() - Wait on in-sync
> + * @sync: Sync object
> + *
> + * If the sync is in an in-sync, wait on the sync to signal.
> + *
> + * Return: 0 on success, -ERESTARTSYS on failure (interruption)
> + */
> +int xe_sync_entry_wait(struct xe_sync_entry *sync)
> +{
> +	if (sync->flags & DRM_XE_SYNC_FLAG_SIGNAL)
> +		return 0;
> +
> +	return dma_fence_wait(sync->fence, true);
> +}
> +
> +/**
> + * xe_sync_needs_wait() - Sync needs a wait (input dma-fence not
> signaled)
> + * @sync: Sync object
> + *
> + * Return: True if sync needs a wait, False otherwise
> + */
> +bool xe_sync_needs_wait(struct xe_sync_entry *sync)
> +{
> +
> +	return !(sync->flags & DRM_XE_SYNC_FLAG_SIGNAL) &&
> +		!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &sync->fence-
> >flags);

dma_fence_is_signaled() ?

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

> +}
> +
>  void xe_sync_entry_signal(struct xe_sync_entry *sync, struct
> dma_fence *fence)
>  {
>  	if (!(sync->flags & DRM_XE_SYNC_FLAG_SIGNAL))
> diff --git a/drivers/gpu/drm/xe/xe_sync.h
> b/drivers/gpu/drm/xe/xe_sync.h
> index 51f2d803e977..6b949194acff 100644
> --- a/drivers/gpu/drm/xe/xe_sync.h
> +++ b/drivers/gpu/drm/xe/xe_sync.h
> @@ -29,6 +29,8 @@ int xe_sync_entry_add_deps(struct xe_sync_entry
> *sync,
>  			   struct xe_sched_job *job);
>  void xe_sync_entry_signal(struct xe_sync_entry *sync,
>  			  struct dma_fence *fence);
> +int xe_sync_entry_wait(struct xe_sync_entry *sync);
> +bool xe_sync_needs_wait(struct xe_sync_entry *sync);
>  void xe_sync_entry_cleanup(struct xe_sync_entry *sync);
>  struct dma_fence *
>  xe_sync_in_fence_get(struct xe_sync_entry *sync, int num_sync,