Am 11.12.24 um 17:14 schrieb Li, Yunxiang (Teddy):
[Public]
From: Koenig, Christian <Christian.Koenig@xxxxxxx>
Sent: Wednesday, December 11, 2024 10:03
Am 11.12.24 um 15:02 schrieb Li, Yunxiang (Teddy):
[Public]
From: Koenig, Christian <Christian.Koenig@xxxxxxx>
Sent: Wednesday, December 11, 2024 3:16 Am 10.12.24 um 18:59 schrieb
Yunxiang Li:
Tracking the state of a GEM object for shared stats is quite
difficult since the handle_count is managed behind driver's back. So
instead considers GEM object shared the moment it is exported with flink ioctl.
This makes it work the same to the dma_buf case. Add a callback for
drivers to get notified when GEM object is being shared.
First of all GEM flink is pretty much deprecated, we only have it for
compatibility reasons. So please don't change anything here.
Then flink is not the only way to create multiple handles for a GEM
object. So this here won't handle all cases.
And finally we already have the .open and .close callbacks, which are
called whenever a handle for a GEM object is created/destroyed. So it
shouldn't be necessary in the first place.
For the importing VM the shared stats is automatically correct by open and close,
but for the exporting VM we need to update the shared stat when the buffer gets
shared, since it is already counted as private there. As far as I could find, seems
like flink ioctl is the only place where the global name is assigned? The importing
side have multiple places to get the global name, but the exporter always needs to
first call flink to allocate the number right? So hooking into flink and dma-buf should
cover the bases?
It's irrelevant where the global name is assigned. The problem is that there are more
ways to create a new handle for a GEM object than just flink and DMA-buf.
For example you can just ask a framebuffer to give you a GEM handle for the
currently displayed buffer. See the call to drm_gem_handle_create() in
drm_mode_getfb2_ioctl().
When you make this change here then those GEM handles are not considered
shared any more even if they are and you sooner or later run into warnings on VM
destruction.
I could probably make handle_count work somehow, but it looks like it's read in a
lot of places without locks so I'm not sure if there will be some race conditions.
The handle count is protected by the object_name_lock of the device. The
drm_gem_object_is_shared_for_memory_stats() function is pretty much the only
case where we read the value without holding the lock since that is used only
opportunistically.
What you could do is to hook into amdgpu_gem_object_open() and
amdgpu_gem_object_close(), call
drm_gem_object_is_shared_for_memory_stats() and go over all the VMs the BO
belongs to. (See how amdgpu_vm_bo_find() and amdgpu_vm_bo_add are used).
Then have an additional flag inside amdgpu_bo_va who tells you if a BO was
previously considered shared or private and update the stats accordingly when that
status changes.
But the open and close functions are called outside the object_name_lock right, so do I regrab the lock in the amdgpu_* functions or I could move the callback into the lock?
You don't need the object_name_lock for this, the update is just
opportunistically.
E.g. you go over all the VMs a BO belongs to and grab the VM spinlock to
update the status in the amdgpu_bo_va structure.
It can in theory be that a concurrent process modifies handle_count at
the same time you update the VM status, but that doesn't matter since
this modification will update the status once more again.
Regards,
Christian.
Regards,
Christian.
Regards,
Christian.
Signed-off-by: Yunxiang Li <Yunxiang.Li@xxxxxxx>
CC: dri-devel@xxxxxxxxxxxxxxxxxxxxx
---
drivers/gpu/drm/drm_gem.c | 3 +++
drivers/gpu/drm/drm_prime.c | 3 +++
include/drm/drm_gem.h | 12 +++++++++++-
3 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index d4bbc5d109c8b..1ead11de31f6b 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -854,6 +854,9 @@ drm_gem_flink_ioctl(struct drm_device *dev, void
*data,
goto err;
obj->name = ret;
+
+ if (obj->funcs->shared)
+ obj->funcs->shared(obj);
}
args->name = (uint64_t) obj->name; diff --git
a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index
0e3f8adf162f6..336d982d69807 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -406,6 +406,9 @@ static struct dma_buf
*export_and_register_object(struct
drm_device *dev,
obj->dma_buf = dmabuf;
get_dma_buf(obj->dma_buf);
+ if (obj->funcs->shared)
+ obj->funcs->shared(obj);
+
return dmabuf;
}
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h index
da11c16e212aa..8c5ffcd485752 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -122,6 +122,16 @@ struct drm_gem_object_funcs {
*/
struct dma_buf *(*export)(struct drm_gem_object *obj, int
flags);
+ /**
+ * @shared:
+ *
+ * Callback when GEM object becomes shared, see also
+ * drm_gem_object_is_shared_for_memory_stats
+ *
+ * This callback is optional.
+ */
+ void (*shared)(struct drm_gem_object *obj);
+
/**
* @pin:
*
@@ -568,7 +578,7 @@ int drm_gem_evict(struct drm_gem_object *obj);
*/
static inline bool
drm_gem_object_is_shared_for_memory_stats(struct
drm_gem_object *obj)
{
- return (obj->handle_count > 1) || obj->dma_buf;
+ return obj->name || obj->dma_buf;
}
#ifdef CONFIG_LOCKDEP
