Re: [PATCH 5/6] drm/xe: Wait on in-syncs when swicthing to dma-fence mode

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

On Fri, Dec 12, 2025 at 07:41:35PM +0100, Thomas Hellström wrote:
> 
> On 12/12/25 17:33, Matthew Brost wrote:
> > On Fri, Dec 12, 2025 at 10:22:54AM +0100, Thomas Hellström wrote:
> > > On Thu, 2025-12-11 at 13:00 -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.
> > > > 
> > > > 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            |  3 ++-
> > > >   drivers/gpu/drm/xe/xe_hw_engine_group.c | 34 +++++++++++++++++++----
> > > > --
> > > >   drivers/gpu/drm/xe/xe_hw_engine_group.h |  4 ++-
> > > >   drivers/gpu/drm/xe/xe_sync.c            | 14 ++++++++++
> > > >   drivers/gpu/drm/xe/xe_sync.h            |  1 +
> > > >   5 files changed, 46 insertions(+), 10 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/xe/xe_exec.c
> > > > b/drivers/gpu/drm/xe/xe_exec.c
> > > > index 4d81210e41f5..5bc598ba6afa 100644
> > > > --- a/drivers/gpu/drm/xe/xe_exec.c
> > > > +++ b/drivers/gpu/drm/xe/xe_exec.c
> > > > @@ -202,7 +202,8 @@ 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_syncs);
> > > >   		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..35966889c776 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;
> > > > @@ -192,20 +194,32 @@ void
> > > > xe_hw_engine_group_resume_faulting_lr_jobs(struct xe_hw_engine_group
> > > > *group
> > > >    *
> > > >    * 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,
> > > > +						       struct
> > > > xe_sync_entry *syncs,
> > > > +						       int
> > > > num_syncs)
> > > >   {
> > > > -	int err;
> > > > +	int err, i;
> > > >   	struct xe_exec_queue *q;
> > > >   	bool need_resume = false;
> > > >   	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;
> > > >   		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);
> > > > +
> > > > +		idle_skip_suspend =
> > > > xe_exec_queue_idle_skip_suspend(q);
> > > > +
> > > > +		if (!need_resume && !idle_skip_suspend && num_syncs)
> > > > {
> > > > +			for (i = 0; i < num_syncs; ++i)
> > > > +				xe_sync_entry_wait(syncs + i);
> > > Here we're in the write-locked mode, right? Ideally I think we should
> > > just check for idle here and return a retry if not idle, and wait
> > > outside of the locks. Perhaps also always wait if there are pf jobs
> > I think waiting outside the lock would be okay. Let me try that. I also
> > forgot that xe_sync_entry_wait needs to be interruptible too.
> > 
> > > running on the engine group. Also we might want to include the other
> > > implicit dependencies as well, like kernel fences.
> > > 
> > > Although perhaps this is good enough for now, and this would be easier
> > > implemented with a scheduler?
> > > 
> This is pretty much exactly what I had in mind as well. I started to doubt,
> though, if the drm scheduler would be a good fit since the dma-fence jobs
> wouldn't necessarily be ordered, since they wouldn't have published their

Yes, if you have mutliple 3d / display users with different sets of
dependencies this starts to fall apart a bit if single scheduler is used
for flipping a group.

> out-fences when in this "pre-scheduler". Also Joonas has mentioned at one
> point that pre-scheduling (like we already do, but this would be a more
> sophisticated version of) was disapproved by some arch or perhaps upstream
> decision at some historical point. We should find out exactly what that was
> all about before proceeding with this.
>

I'm not exactly following this part of if we circle back to this, I can
dig in here.

> > This is a fairly large rework, and the likelihood of me personally
> > having the bandwidth to implement this in the near future is low. Of
> > course, if you want to take this on, I can provide guidance on the
> > refactor.
> 
> My bandwidth for this is also zero ATM and up to end of January at least.
> 

Mine too. If someone else in group wants to pick it up, that would work too.

> > So for now, let’s tweak things to something we can live with and perhaps
> > write down plans for a long-term refactor.
> 
> Fully agree.
> 
> I think our backlog of nice cleanups and improvements like this is starting
> to grow so it would be good to have them documented in jiras and perhaps at
> a list which we can prioritze and have someone pick up when there is
> bandwidth.
> 

+1. Yes, I'd prefer stay on top of clean ups to avoid driver becoming
unmanagable mess.

Matt


> Thanks,
> 
> Thomas
> 
> 
> 
> > 
> > Matt
> > 
> > > /Thomas
> > > 
> > > 
> > > > +		}
> > > > +
> > > > +		need_resume |= !idle_skip_suspend;
> > > >   		q->ops->suspend(q);
> > > >   	}
> > > > @@ -258,7 +272,8 @@ 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,
> > > > +		       struct xe_sync_entry *syncs, int num_syncs)
> > > >   {
> > > >   	int err = 0;
> > > >   	enum xe_hw_engine_group_execution_mode new_mode;
> > > > @@ -268,7 +283,9 @@ 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,
> > > > +								
> > > > syncs,
> > > > +								
> > > > num_syncs);
> > > >   		break;
> > > >   	case EXEC_MODE_DMA_FENCE:
> > > >   		new_mode = EXEC_MODE_LR;
> > > > @@ -294,7 +311,8 @@ static int switch_mode(struct xe_hw_engine_group
> > > > *group)
> > > >    */
> > > >   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)
> > > >   {
> > > >   	int err = down_read_interruptible(&group->mode_sem);
> > > > @@ -311,7 +329,7 @@ __acquires(&group->mode_sem)
> > > >   			return err;
> > > >   		if (new_mode != group->cur_mode) {
> > > > -			err = switch_mode(group);
> > > > +			err = switch_mode(group, syncs, num_syncs);
> > > >   			if (err) {
> > > >   				up_write(&group->mode_sem);
> > > >   				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..127e26129933 100644
> > > > --- a/drivers/gpu/drm/xe/xe_sync.c
> > > > +++ b/drivers/gpu/drm/xe/xe_sync.c
> > > > @@ -228,6 +228,20 @@ 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.
> > > > + */
> > > > +void xe_sync_entry_wait(struct xe_sync_entry *sync)
> > > > +{
> > > > +	if (sync->flags & DRM_XE_SYNC_FLAG_SIGNAL)
> > > > +		return;
> > > > +
> > > > +	dma_fence_wait(sync->fence, false);
> > > > +}
> > > > +
> > > >   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..1c08f9ed9001 100644
> > > > --- a/drivers/gpu/drm/xe/xe_sync.h
> > > > +++ b/drivers/gpu/drm/xe/xe_sync.h
> > > > @@ -29,6 +29,7 @@ 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);
> > > > +void xe_sync_entry_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,