[Mesa-dev] [PATCH 2/2] i965: Context aware user space EU control through application

[Marathe, Yogesh]

Lionel, Chris,

> -----Original Message-----
> From: mesa-dev [mailto:mesa-dev-bounces at lists.freedesktop.org] On Behalf
> Of Lionel Landwerlin
> Sent: Friday, July 20, 2018 3:31 PM
> To: Chris Wilson <chris at chris-wilson.co.uk>; Muthukumar, Aravindan
> <aravindan.muthukumar at intel.com>; mesa-dev at lists.freedesktop.org
> Subject: Re: [Mesa-dev] [PATCH 2/2] i965: Context aware user space EU control
> through application
> 
> On 20/07/18 09:47, Chris Wilson wrote:
> > Quoting aravindan.muthukumar at intel.com (2018-07-20 09:32:57)
> >> From: "Muthukumar, Aravindan" <aravindan.muthukumar at intel.com>
> >>
> >>   The Patch here is to give control to user/ application to really
> >>   decide what's the max GPU load it would put. If that can be
> >>   known in advance, rpcs can be programmed accordingly.
> >>   This solution has changes across i915,
> >>   drm and mesa (not limited only to kernel).
> >>
> >>   Here, we pass gpu_load_type = {high, medium, low} from application
> >>   while context is created. Default here is 'High' and applications
> >>   roughly know if they are going to eat up entire GPU. The typical
> >>   usecase of 'Low' is idle screen or minor mouse movements. Users can
> >>   read meaning of high/medium/low for their platform  & then program
> >>   contexts accordingly. Here gpu_load_type directly translates to
> >>   number of shader cores/EUs a particular GPU has.
> >>
> >>   Signed-off-by: Aravindan Muthukumar <aravindan.muthukumar at intel.com>
> >>   Signed-off-by: Kedar J Karanje <kedar.j.karanje at intel.com>
> >>   Signed-off-by: Praveen Diwakar <praveen.diwakar at intel.com>
> >>   Signed-off-by: Yogesh Marathe <yogesh.marathe at intel.com>
> >> +/* Dynamic Eu control */
> >> +struct drm_i915_load_type {
> >> +       __u32 ctx_id;
> >> +       __u32 load_type;
> >> +};
> >> +
> >> +/* DYNAMIC EU CONTROL */
> >> +int
> >> +brw_hw_context_load_type(struct brw_bufmgr *bufmgr,
> >> +                        uint32_t ctx_id,
> >> +                        int load_type) {
> >> +       struct drm_i915_load_type type = {
> >> +               .ctx_id = ctx_id,
> >> +               .load_type = load_type,
> >> +       };
> >> +       int err;
> >> +
> >> +       err = 0;
> >> +       if(drmIoctl(bufmgr->fd, DRM_IOCTL_I915_LOAD_TYPE, &type))
> >> +               err = -errno;
> > This went through 4 people and none noticed that there already exists
> > a means to set per-context parameters. And it's even used right next
> > to this function.
> >
> > The word hint needs to be firmly embedded around here.
> > -Chris
> > ______
> 
> Yep,
> 
> Looks like you want to get involved in this discussion :
> https://patchwork.freedesktop.org/series/42285/

I understand this is exposing per context eu config through debugfs. That mostly
(if not fully) matches the  kernel part of what we wanted to achieve. We have 
additional code in kernel where we categorize based on load type and fix 
a config per platform. For sure the kernel parts can be merged but the proposal 
is different here and its specific to adding this capability through mesa.

Here we are enabling applications to decide load while creating the context and 
making it simple for application programmers by abstracting it.  Also in these kernel 
patches, its seems to be exposing the parameters to user space, are we discussing 
its user space counterpart in mesa or in some other component? If not, I feel this
is bit different. Can it be a mesa extension? Then any app / process can do this
without having privilege (root).

> 
> -
> Lionel
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