[Intel-gfx] [PATCH RFC 2/5] cgroup: Add mechanism to register vendor specific DRM devices

[Ho, Kenny]

On Wed, Nov 28, 2018 at 4:14 AM Joonas Lahtinen <joonas.lahtinen at linux.intel.com> wrote:
> So we can only choose the lowest common denominator, right?
>
> Any core count out of total core count should translate nicely into a
> fraction, so what would be the problem with percentage amounts?

I don't think having an abstracted resource necessarily equate 'lowest'.  The issue with percentage is the lack of precision.  If you look at cpuset cgroup, you can see the specification can be very precise:

# /bin/echo 1-4,6 > cpuset.cpus -> set cpus list to cpus 1,2,3,4,6
(https://www.kernel.org/doc/Documentation/cgroup-v1/cpusets.txt)

The driver can translate something like this to core count and then to percentage and handle accordingly while the reverse is not possible.  (You can't tell which set of CUs/EUs a user want from a percentage request.)  It's also not clear to me, from user/application/admin/resource management perspective, how the base core counts of a GPU is relevant to the workload (since percentage is a 'relative' quantity.)  For example, let say a workload wants to use 256 'cores', does it matter if that workload is put on a GPU with 1024 cores or a GPU with 4096 cores total?

I am not dismissing the possible need for percentage.  I just think there should be a way to accommodate more than just the 'lowest'. 

Regards,
Kennny


> > > That combined with the "GPU memory usable" property should be a good
> > > starting point to start subdividing the GPU resources for multiple
> > > users.
> > >
> > > Regards, Joonas
> > >
> > > >
> > > > Your feedback is highly appreciated.
> > > >
> > > > Best Regards,
> > > > Harish
> > > >
> > > >
> > > >
> > > > From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> on behalf of Tejun Heo <tj at kernel.org>
> > > > Sent: Tuesday, November 20, 2018 5:30 PM
> > > > To: Ho, Kenny
> > > > Cc: cgroups at vger.kernel.org; intel-gfx at lists.freedesktop.org; y2kenny at gmail.com; amd-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org
> > > > Subject: Re: [PATCH RFC 2/5] cgroup: Add mechanism to register vendor specific DRM devices
> > > >
> > > >
> > > > Hello,
> > > >
> > > > On Tue, Nov 20, 2018 at 10:21:14PM +0000, Ho, Kenny wrote:
> > > > > By this reply, are you suggesting that vendor specific resources
> > > > > will never be acceptable to be managed under cgroup?  Let say a user
> > > >
> > > > I wouldn't say never but whatever which gets included as a cgroup
> > > > controller should have clearly defined resource abstractions and the
> > > > control schemes around them including support for delegation.  AFAICS,
> > > > gpu side still seems to have a long way to go (and it's not clear
> > > > whether that's somewhere it will or needs to end up).
> > > >
> > > > > want to have similar functionality as what cgroup is offering but to
> > > > > manage vendor specific resources, what would you suggest as a
> > > > > solution?  When you say keeping vendor specific resource regulation
> > > > > inside drm or specific drivers, do you mean we should replicate the
> > > > > cgroup infrastructure there or do you mean either drm or specific
> > > > > driver should query existing hierarchy (such as device or perhaps
> > > > > cpu) for the process organization information?
> > > > >
> > > > > To put the questions in more concrete terms, let say a user wants to
> > > > > expose certain part of a gpu to a particular cgroup similar to the
> > > > > way selective cpu cores are exposed to a cgroup via cpuset, how
> > > > > should we go about enabling such functionality?
> > > >
> > > > Do what the intel driver or bpf is doing?  It's not difficult to hook
> > > > into cgroup for identification purposes.
> > > >
> > > > Thanks.
> > > >
> > > > --
> > > > tejun
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