Quoting Chris Wilson (2018-03-08 11:32:04)
Quoting Matt Roper (2018-03-06 23:46:59)
There are cases where a system integrator may wish to raise/lower the priority of GPU workloads being submitted by specific OS process(es), independently of how the software self-classifies its own priority. Exposing "priority offset" as an i915-specific cgroup parameter will enable such system-level configuration.
Normally GPU contexts start with a priority value of 0 (I915_CONTEXT_DEFAULT_PRIORITY) and then may be adjusted up/down from there via other mechanisms. We'd like to provide a system-level input to the priority decision that will be taken into consideration, even when userspace later attempts to set an absolute priority value via I915_CONTEXT_PARAM_PRIORITY. The priority offset introduced here provides a base value that will always be added to (or subtracted from) the software's self-assigned priority value.
This patch makes priority offset a cgroup-specific value; contexts will be created with a priority offset based on the cgroup membership of the process creating the context at the time the context is created. Note that priority offset is assigned at context creation time; migrating a process to a different cgroup or changing the offset associated with a cgroup will only affect new context creation and will not alter the behavior of existing contexts previously created by the process.
v2:
- Rebase onto new cgroup_priv API
- Use current instead of drm_file->pid to determine which process to lookup priority for. (Chris)
- Don't forget to subtract priority offset in context_getparam ioctl to make it match setparam behavior. (Chris)
Signed-off-by: Matt Roper matthew.d.roper@intel.com
For ctx->priority/ctx->priority_offset Reviewed-by: Chris Wilson chris@chris-wilson.co.uk
As a reminder, we do have the question of how to bound ctx->priority + ctx->priority_offset. Currently, outside of the user range is privileged space reserved for the kernel (both above and below). Now we can move those even further to accommodate multiple non-overlapping cgroups. We also have the presumption that only privileged processes can raise a priority, but I presume the cgroup property itself is protected. -Chris