Re: [PATCH v3 13/13] drm/i915/scheduler: Support user-defined priorities

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On Thu, 2017-09-28 at 20:39 +0100, Chris Wilson wrote:
> Use a priority stored in the context as the initial value when
> submitting a request. This allows us to change the default priority on a
> per-context basis, allowing different contexts to be favoured with GPU
> time at the expense of lower importance work. The user can adjust the
> context's priority via I915_CONTEXT_PARAM_PRIORITY, with more positive
> values being higher priority (they will be serviced earlier, after their
> dependencies have been resolved). Any prerequisite work for an execbuf
> will have its priority raised to match the new request as required.
> 
> Normal users can specify any value in the range of -1023 to 0 [default],
> i.e. they can reduce the priority of their workloads (and temporarily
> boost it back to normal if so desired).
> 
> Privileged users can specify any value in the range of -1023 to 1023,
> [default is 0], i.e. they can raise their priority above all overs and
> so potentially starve the system.
> 
> Note that the existing schedulers are not fair, nor load balancing, the
> execution is strictly by priority on a first-come, first-served basis,
> and the driver may choose to boost some requests above the range
> available to users.
> 
> This priority was originally based around nice(2), but evolved to allow
> clients to adjust their priority within a small range, and allow for a
> privileged high priority range.
> 
> For example, this can be used to implement EGL_IMG_context_priority
> https://www.khronos.org/registry/egl/extensions/IMG/EGL_IMG_context_priority.txt
> 
> 	EGL_CONTEXT_PRIORITY_LEVEL_IMG determines the priority level of
>         the context to be created. This attribute is a hint, as an
>         implementation may not support multiple contexts at some
>         priority levels and system policy may limit access to high
>         priority contexts to appropriate system privilege level. The
>         default value for EGL_CONTEXT_PRIORITY_LEVEL_IMG is
>         EGL_CONTEXT_PRIORITY_MEDIUM_IMG."
> 
> so we can map
> 
> 	PRIORITY_HIGH -> 1023 [privileged, will failback to 0]
> 	PRIORITY_MED -> 0 [default]
> 	PRIORITY_LOW -> -1023
> 
> They also map onto the priorities used by VkQueue (and a VkQueue is
> essentially a timeline, our i915_gem_context under full-ppgtt).
> 
> v2: s/CAP_SYS_ADMIN/CAP_SYS_NICE/
> v3: Report min/max user priorities as defines in the uapi, and rebase
> internal priorities on the exposed values.
> 
> Testcase: igt/gem_exec_schedule
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Didn't seem to stick last time :P

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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