On 7/13/26 13:57, Thomas Hellström wrote:
> On Fri, 2026-07-10 at 20:52 +0200, Christian König wrote:
>> Restructure the drm_exec object to work with dma_resv references
>> instead
>> of GEM object references.
>>
>> Add the new function dma_exec_lock_resv() to lock individual dma_resv
>> objects and so allow higher level implementations to handle
>> contention
>> purely on dma_resv objects.
>>
>> WIP! Don't commit like that!
>>
>> Signed-off-by: Christian König <[email protected]>
>
> Here, IMO we should move a dma-resv based implementation to dma-buf to
> facilitate passing it also through dma_buf_map(),
I still don't see why that would be necessary?
dma_buf_map() just maps the current location of the buffer, it has no
requirement to force the buffer into VRAM.
At least on amdgpu we always validate buffer during dma_buf_map() with
VRAM|GTT, so we never cause any eviction at all.
> And if wanting to avoid rewriting all users of drm_exec, Make drm_exec
> a thin wrapper on top.
DMA-buf looks like the wrong place for this since it only works on exported
buffers and that should be the absolute minority.
We could have a dma-resv contention tracking helper, but I still don't see for
what that would be good for?
Regards,
Christian.
>
> Thanks,
> Thomas
>
>
>
>> ---
>> drivers/gpu/drm/drm_exec.c | 75 ++++++++++++++++++++++--------------
>> --
>> drivers/gpu/drm/drm_gem.c | 2 +
>> include/drm/drm_exec.h | 9 +++--
>> 3 files changed, 50 insertions(+), 36 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_exec.c b/drivers/gpu/drm/drm_exec.c
>> index fa923852fae45..382bf7bcd5ff3 100644
>> --- a/drivers/gpu/drm/drm_exec.c
>> +++ b/drivers/gpu/drm/drm_exec.c
>> @@ -58,8 +58,11 @@ static void drm_exec_unlock_all(struct drm_exec
>> *exec)
>> drm_gem_object_put(obj);
>> }
>>
>> - drm_gem_object_put(exec->prelocked);
>> - exec->prelocked = NULL;
>> + if (exec->prelocked) {
>> + dma_resv_unlock(exec->prelocked);
>> + dma_resv_put(exec->prelocked);
>> + exec->prelocked = NULL;
>> + }
>> }
>>
>> /**
>> @@ -101,7 +104,7 @@ void drm_exec_fini(struct drm_exec *exec)
>> drm_exec_unlock_all(exec);
>> kvfree(exec->objects);
>> if (exec->contended != DRM_EXEC_DUMMY) {
>> - drm_gem_object_put(exec->contended);
>> + dma_resv_put(exec->contended);
>> ww_acquire_fini(&exec->ticket);
>> }
>> }
>> @@ -158,50 +161,41 @@ static int drm_exec_obj_locked(struct drm_exec
>> *exec,
>> /* Make sure the contended object is locked first */
>> static int drm_exec_lock_contended(struct drm_exec *exec)
>> {
>> - struct drm_gem_object *obj = exec->contended;
>> + struct dma_resv *resv = exec->contended;
>> int ret;
>>
>> - if (likely(!obj))
>> + if (likely(!resv))
>> return 0;
>>
>> /* Always cleanup the contention so that error handling can
>> kick in */
>> exec->contended = NULL;
>> if (exec->flags & DRM_EXEC_INTERRUPTIBLE_WAIT) {
>> - ret = dma_resv_lock_slow_interruptible(obj->resv,
>> - &exec-
>>> ticket);
>> + ret = dma_resv_lock_slow_interruptible(resv, &exec-
>>> ticket);
>> if (unlikely(ret))
>> goto error_dropref;
>> } else {
>> - dma_resv_lock_slow(obj->resv, &exec->ticket);
>> + dma_resv_lock_slow(resv, &exec->ticket);
>> }
>>
>> - ret = drm_exec_obj_locked(exec, obj);
>> - if (unlikely(ret))
>> - goto error_unlock;
>> -
>> - exec->prelocked = obj;
>> + exec->prelocked = resv;
>> return 0;
>>
>> -error_unlock:
>> - dma_resv_unlock(obj->resv);
>> -
>> error_dropref:
>> - drm_gem_object_put(obj);
>> + dma_resv_put(resv);
>> return ret;
>> }
>>
>> /**
>> - * drm_exec_lock_obj - lock a GEM object for use
>> + * drm_exec_lock_resv - lock a dma_resv object
>> * @exec: the drm_exec object with the state
>> - * @obj: the GEM object to lock
>> + * @resv: the dma_resv object to lock
>> *
>> - * Lock a GEM object for use and grab a reference to it.
>> + * Lock a dma_resv object for use or grab a reference to it on
>> contention.
>> *
>> * Returns: -EDEADLK if a contention is detected, -EALREADY when
>> object is
>> - * already locked (can be suppressed by setting the
>> DRM_EXEC_IGNORE_DUPLICATES
>> - * flag), -ENOMEM when memory allocation failed and zero for
>> success.
>> + * already locked, -ENOMEM when memory allocation failed and zero
>> for success.
>> */
>> -int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object
>> *obj)
>> +int drm_exec_lock_resv(struct drm_exec *exec, struct dma_resv *resv)
>> {
>> int ret;
>>
>> @@ -209,22 +203,39 @@ int drm_exec_lock_obj(struct drm_exec *exec,
>> struct drm_gem_object *obj)
>> if (unlikely(ret))
>> return ret;
>>
>> - if (exec->prelocked == obj) {
>> - drm_gem_object_put(exec->prelocked);
>> + if (exec->prelocked == resv) {
>> + dma_resv_put(exec->prelocked);
>> exec->prelocked = NULL;
>> return 0;
>> }
>>
>> if (exec->flags & DRM_EXEC_INTERRUPTIBLE_WAIT)
>> - ret = dma_resv_lock_interruptible(obj->resv, &exec-
>>> ticket);
>> + ret = dma_resv_lock_interruptible(resv, &exec-
>>> ticket);
>> else
>> - ret = dma_resv_lock(obj->resv, &exec->ticket);
>> + ret = dma_resv_lock(resv, &exec->ticket);
>>
>> - if (unlikely(ret == -EDEADLK)) {
>> - drm_gem_object_get(obj);
>> - exec->contended = obj;
>> - return -EDEADLK;
>> - }
>> + if (unlikely(ret == -EDEADLK))
>> + exec->contended = dma_resv_get(resv);
>> + return ret;
>> +}
>> +EXPORT_SYMBOL(drm_exec_lock_resv);
>> +
>> +/**
>> + * drm_exec_lock_obj - lock a GEM object for use
>> + * @exec: the drm_exec object with the state
>> + * @obj: the GEM object to lock
>> + *
>> + * Lock a GEM object for use and grab a reference to it.
>> + *
>> + * Returns: -EDEADLK if a contention is detected, -EALREADY when
>> object is
>> + * already locked (can be suppressed by setting the
>> DRM_EXEC_IGNORE_DUPLICATES
>> + * flag), -ENOMEM when memory allocation failed and zero for
>> success.
>> + */
>> +int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object
>> *obj)
>> +{
>> + int ret;
>> +
>> + ret = drm_exec_lock_resv(exec, obj->resv);
>>
>> if (unlikely(ret == -EALREADY) &&
>> exec->flags & DRM_EXEC_IGNORE_DUPLICATES)
>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>> index bbcbd25f014f0..f5cf9ad596a67 100644
>> --- a/drivers/gpu/drm/drm_gem.c
>> +++ b/drivers/gpu/drm/drm_gem.c
>> @@ -229,6 +229,8 @@ void drm_gem_private_object_init(struct
>> drm_device *dev,
>> obj->size = size;
>> mutex_init(&obj->gpuva.lock);
>> dma_resv_init(&obj->_resv);
>> +
>> + /* TODO: This needs to go away for drm_exec to work
>> correctly!!! */
>> if (!obj->resv)
>> obj->resv = dma_resv_get(&obj->_resv);
>>
>> diff --git a/include/drm/drm_exec.h b/include/drm/drm_exec.h
>> index 8725ba92ff916..9daedb676d7b1 100644
>> --- a/include/drm/drm_exec.h
>> +++ b/include/drm/drm_exec.h
>> @@ -47,14 +47,14 @@ struct drm_exec {
>> struct drm_gem_object **objects;
>>
>> /**
>> - * @contended: contended GEM object we backed off for
>> + * @contended: contended dma_resv object we backed off for
>> */
>> - struct drm_gem_object *contended;
>> + struct dma_resv *contended;
>>
>> /**
>> - * @prelocked: already locked GEM object due to contention
>> + * @prelocked: already locked dma_resv object due to
>> contention
>> */
>> - struct drm_gem_object *prelocked;
>> + struct dma_resv *prelocked;
>> };
>>
>> /**
>> @@ -175,6 +175,7 @@ static inline struct ww_acquire_ctx
>> *drm_exec_ticket(struct drm_exec *exec)
>> void drm_exec_init(struct drm_exec *exec, u32 flags, unsigned nr);
>> void drm_exec_fini(struct drm_exec *exec);
>> bool drm_exec_cleanup(struct drm_exec *exec);
>> +int drm_exec_lock_resv(struct drm_exec *exec, struct dma_resv
>> *resv);
>> int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object
>> *obj);
>> void drm_exec_unlock_obj(struct drm_exec *exec, struct
>> drm_gem_object *obj);
>> int drm_exec_prepare_obj(struct drm_exec *exec, struct
>> drm_gem_object *obj,
