Am 22.06.23 um 17:07 schrieb Danilo Krummrich:
On 6/22/23 17:04, Danilo Krummrich wrote:
On 6/22/23 16:42, Christian König wrote:
Am 22.06.23 um 16:22 schrieb Danilo Krummrich:
On 6/22/23 15:54, Christian König wrote:
Am 20.06.23 um 14:23 schrieb Danilo Krummrich:
Hi Christian,
On 6/20/23 08:45, Christian König wrote:
Hi Danilo,
sorry for the delayed reply. I've trying to dig myself out of a
hole at the moment.
No worries, thank you for taking a look anyway!
Am 20.06.23 um 02:42 schrieb Danilo Krummrich:
[SNIP]
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index bbc721870c13..5ec8148a30ee 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -36,6 +36,8 @@
#include <linux/kref.h>
#include <linux/dma-resv.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
#include <drm/drm_vma_manager.h>
@@ -379,6 +381,18 @@ struct drm_gem_object {
*/
struct dma_resv _resv;
+ /**
+ * @gpuva:
+ *
+ * Provides the list of GPU VAs attached to this GEM object.
+ *
+ * Drivers should lock list accesses with the GEMs
&dma_resv lock
+ * (&drm_gem_object.resv).
+ */
+ struct {
+ struct list_head list;
+ } gpuva;
+
/**
* @funcs:
*
I'm pretty sure that it's not a good idea to attach this
directly to the GEM object.
Why do you think so? IMHO having a common way to connect mappings
to their backing buffers is a good thing, since every driver
needs this connection anyway.
E.g. when a BO gets evicted, drivers can just iterate the list of
mappings and, as the circumstances require, invalidate the
corresponding mappings or to unmap all existing mappings of a
given buffer.
What would be the advantage to let every driver implement a
driver specific way of keeping this connection?
Flexibility. For example on amdgpu the mappings of a BO are groups
by VM address spaces.
E.g. the BO points to multiple bo_vm structures which in turn have
lists of their mappings.
Isn't this (almost) the same relationship I introduce with the
GPUVA manager?
If you would switch over to the GPUVA manager right now, it would
be that every GEM has a list of it's mappings (the gpuva list). The
mapping is represented by struct drm_gpuva (of course embedded in
driver specific structure(s)) which has a pointer to the VM address
space it is part of, namely the GPUVA manager instance. And the
GPUVA manager keeps a maple tree of it's mappings as well.
If you still would like to *directly* (indirectly you already have
that relationship) keep a list of GPUVA managers (VM address
spaces) per GEM, you could still do that in a driver specific way.
Do I miss something?
How do you efficiently find only the mappings of a BO in one VM?
Actually, I think this case should even be more efficient than with a
BO having a list of GPUVAs (or mappings):
*than with a BO having a list of VMs:
Having a list of GPUVAs per GEM, each GPUVA has a pointer to it's VM.
Hence, you'd only need to iterate the list of mappings for a given BO
and check the mappings VM pointer.
Yeah, and that is extremely time consuming if you have tons of mappings
in different VMs.
Having a list of VMs per BO, you'd have to iterate the whole VM to
find the mappings having a pointer to the given BO, right?
No, you don't seem to understand what I'm suggesting.
Currently you have a list of mappings attached to the BO, so when you
need to make sure that a specific BO is up to date in a specific VM you
either need to iterate over the VM or the BO. Neither of that is a good
idea.
What you need is a representation of the data used for each BO+VM
combination. In other words another indirection which allows you to
handle all the mappings of a BO inside a VM at once.
I'd think that a single VM potentially has more mapping entries than
a single BO was mapped in multiple VMs.
Another case to consider is the case I originally had in mind
choosing this relationship: finding all mappings for a given BO,
which I guess all drivers need to do in order to invalidate mappings
on BO eviction.
Having a list of VMs per BO, wouldn't you need to iterate all of the
VMs entirely?
No, see how amdgpu works.
Regards,
Christian.
