[PATCH RFC v4 14/16] drm, cgroup: Introduce lgpu as DRM cgroup resource

tj at kernel.org tj at kernel.org
Fri Oct 11 17:12:47 UTC 2019

Hello, Daniel.

On Wed, Oct 09, 2019 at 06:06:52PM +0200, Daniel Vetter wrote:
> That's not the point I was making. For cpu cgroups there's a very well
> defined connection between the cpu bitmasks/numbers in cgroups and the cpu
> bitmasks you use in various system calls (they match). And that stuff
> works across vendors.

Please note that there are a lot of limitations even to cpuset.
Affinity is easy to implement and seems attractive in terms of
absolute isolation but it's inherently cumbersome and limited in
granularity and can lead to surprising failure modes where contention
on one cpu can't be resolved by the load balancer and leads to system
wide slowdowns / stalls caused by the dependency chain anchored at the
affinity limited tasks.

Maybe this is a less of a problem for gpu workloads but in general the
more constraints are put on scheduling, the more likely is the system
to develop twisted dependency chains while other parts of the system
are sitting idle.

How does scheduling currently work when there are competing gpu
workloads?  There gotta be some fairness provision whether that's unit
allocation based or time slicing, right?  If that's the case, it might
be best to implement proportional control on top of that.
Work-conserving mechanisms are the most versatile, easiest to use and
least likely to cause regressions.



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