Hello,
On Wed, Jul 26, 2023 at 12:14:24PM +0200, Maarten Lankhorst wrote:
So, yeah, if you want to add memory controls, we better think
through how
the fd ownership migration should work.
I've taken a look at the series, since I have been working on cgroup
memory
eviction.
The scheduling stuff will work for i915, since it has a purely software
execlist scheduler, but I don't think it will work for GuC (firmware)
scheduling or other drivers that use the generic drm scheduler.
For something like this, you would probably want it to work inside
the drm
scheduler first. Presumably, this can be done by setting a weight on
each
runqueue, and perhaps adding a callback to update one for a running
queue.
Calculating the weights hierarchically might be fun..
I don't have any idea on this front. The basic idea of making high level
distribution decisions in core code and letting individual drivers
enforce
that in a way which fits them the best makes sense to me but I don't know
enough to have an opinion here.
I have taken a look at how the rest of cgroup controllers change
ownership
when moved to a different cgroup, and the answer was: not at all. If we
For persistent resources, that's the general rule. Whoever instantiates a
resource gets to own it until the resource gets freed. There is an
exception
with the pid controller and there are discussions around whether we want
some sort of migration behavior with memcg but yes by and large
instantiator
being the owner is the general model cgroup follows.
attempt to create the scheduler controls only on the first time the
fd is
used, you could probably get rid of all the tracking.
This can be done very easily with the drm scheduler.
WRT memory, I think the consensus is to track system memory like normal
memory. Stolen memory doesn't need to be tracked. It's kernel only
memory,
used for internal bookkeeping only.
The only time userspace can directly manipulate stolen memory, is by
mapping
the pinned initial framebuffer to its own address space. The only
allocation
it can do is when a framebuffer is displayed, and framebuffer
compression
creates some stolen memory. Userspace is not
aware of this though, and has no way to manipulate those contents.
So, my dumb understanding:
* Ownership of an fd can be established on the first ioctl call and
doesn't
need to be migrated afterwards. There are no persistent resources to
migration on the first call.
