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

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

On Mon, Dec 15, 2025 at 11:32:23AM +0100, Thomas Hellström wrote:
> 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() ?
> 

I don't want to signal the fence here, Phillip Stanner merged a
dma-fence helper that does this check to drm-misc-next but this change
hasn't made it to dma-xe-next yet. I have patch built on top of his
series to to convert Xe to use these helpers, when I rebase that patch
I'll fixup this code too.

Matt 

> 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,
>