[Intel-gfx] DRM cgroups integration (Was: Re: [PATCH v4 0/8] cgroup private data and DRM/i915 integration)

Thu Apr 5 15:06:23 UTC 2018

On Thu, Apr 05, 2018 at 07:49:44AM -0700, Matt Roper wrote:
> On Thu, Apr 05, 2018 at 05:15:13PM +0300, Joonas Lahtinen wrote:
> > + Some more Cc's based on IRC discussion
> > 
> > Quoting Joonas Lahtinen (2018-04-05 16:46:51)
> > > + Dave for commenting from DRM subsystem perspective. I strongly believe
> > > there would be benefit from agreeing on some foundation of DRM subsystem
> > > level program GPU niceness [-20,19] and memory limit [0,N] pages.
> 
> +Chris Wilson

+more Cc's based on IRC discussion.


Matt

> 
> If we ignore backward compatibility and ABI issues for now and assume
> all drivers can move to [-20, 19] for application-accessible priority
> ranges (i.e., self opt-in via existing context parameter ioctls and
> such), I think we still need a much larger range for the priority offset
> assigned via cgroup.  One of the goals with the cgroup work is to give
> the system integrator the ability to define classes of applications with
> non-overlapping ranges (i.e., in some systems an app in the "very
> important" cgroup that self-lowers itself as far as possible should
> still be prioritized higher than an app in the "best effort" cgroup that
> self-boosts itself as far as possible).  Chris Wilson and I discussed
> that a bit on this thread if you want to see the context:
> 
> https://lists.freedesktop.org/archives/intel-gfx/2018-March/158204.html
> 
> That discussion was based on i915's current application-accessible range
> of [-1023,1023].  If we shift to a much smaller [-20,19] range for
> applications to use directly, then we might want to allow cgroup offset
> to be something like [-1000,1000] to ensure the system integrator has
> enough flexibility?
> 
> Also note that "display boost" (i.e., a priority boost for contexts that
> are blocking a flip) may vary depending on system setup, so setting
> being able to define the display boost's effective priority via cgroup
> is important as well.
> 
> 
> Matt
> 
> 
> 
> > > 
> > > Quoting Matt Roper (2018-03-30 03:43:13)
> > > > On Mon, Mar 26, 2018 at 10:30:23AM +0300, Joonas Lahtinen wrote:
> > > > > Quoting Matt Roper (2018-03-23 17:46:16)
> > > > > > On Fri, Mar 23, 2018 at 02:15:38PM +0200, Joonas Lahtinen wrote:
> > > > > > > Quoting Matt Roper (2018-03-17 02:08:57)
> > > > > > > > This is the fourth iteration of the work previously posted here:
> > > > > > > >   (v1) https://lists.freedesktop.org/archives/intel-gfx/2018-January/153156.html
> > > > > > > >   (v2) https://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg208170.html
> > > > > > > >   (v3) https://lists.freedesktop.org/archives/intel-gfx/2018-March/157928.html
> > > > > > > > 
> > > > > > > > The high level goal of this work is to allow non-cgroup-controller parts
> > > > > > > > of the kernel (e.g., device drivers) to register their own private
> > > > > > > > policy data for specific cgroups.  That mechanism is then made use of in
> > > > > > > > the i915 graphics driver to allow GPU priority to be assigned according
> > > > > > > > to the cgroup membership of the owning process.  Please see the v1 cover
> > > > > > > > letter linked above for a more in-depth explanation and justification.
> > > > > > > 
> > > > > > > Hi Matt,
> > > > > > > 
> > > > > > > For cross-subsystem changes such as this, it makes sense to Cc all
> > > > > > > relevant maintainers, especially if there have been previous comments to
> > > > > > > earlier revisions.
> > > > > > > 
> > > > > > > Please, do include and keep a reference to the userspace portion of the
> > > > > > > changes when you suggest new uAPI to be added. At least I have some trouble
> > > > > > > trying to track down the relevant interface consumer here.
> > > > > > > 
> > > > > > > I'm unsure how much sense it makes to commence with detailed i915 review
> > > > > > > if we will be blocked by lack of userspace after that? I'm assuming
> > > > > > > you've read through [1] already.
> > > > > > 
> > > > > > Hi Joonas,
> > > > > > 
> > > > > > I've sent the userspace code out a few times, but it looks like I forgot
> > > > > > to include a copy with v4/v4.5.  Here's the version I provided with v3:
> > > > > >   https://lists.freedesktop.org/archives/intel-gfx/2018-March/157935.html
> > > > > 
> > > > > Thanks. Keeping that in the relevant commit message of the patch that
> > > > > introduces the new uAPI will make it harder to forget and easiest for
> > > > > git blame, too.
> > > > > 
> > > > > > 
> > > > > > Usually we don't consider things like i-g-t to be sufficient userspace
> > > > > > consumers because we need a real-world consumer rather than a "toy"
> > > > > > userspace.  However in this case, the i-g-t tool, although very simple,
> > > > > > is really the only userspace consumer I expect there to ever be.
> > > > > > Ultimately the true consumer of this cgroups work are bash scripts, sysv
> > > > > > init scripts, systemd recipes, etc.  that just need a very simple tool
> > > > > > to assign the specific values that make sense on a given system.
> > > > > > There's no expectation that graphics clients or display servers would
> > > > > > ever need to make use of these interfaces.
> > > > > 
> > > > > I was under the impression that a bit more generic GPU cgroups support
> > > > > was receiving a lot of support in the early discussion? A dedicated
> > > > > intel_cgroup sounds underwhelming, when comparing to idea of "gpu_nice",
> > > > > for user adoption :)
> > > > 
> > > > I'm open to moving the cgroup_priv registration/lookup to the DRM core
> > > > if other drivers are interested in using this mechanism and if we can
> > > > come to an agreement on a standard priority offset range to support, how
> > > > display boost should work for all drivers, etc.  There might be some
> > > > challenges mapping a DRM-defined priority range down to a different
> > > > range that makes sense for individual driver schedulers, especially
> > > > since some drivers already expose a different priority scheme to
> > > > userspace via other interfaces like i915 does with GEM context priority.
> > > > 
> > > > So far I haven't really heard any interest outside the Intel camp, but
> > > > hopefully other driver teams can speak up if they're for/against this.
> > > > I don't want to try to artificially standardize this if other drivers
> > > > want to go a different direction with priority/scheduling that's too
> > > > different from the current Intel-driven design.
> > > 
> > > I don't think there are that many directions to go about GPU context
> > > priority, considering we have the EGL_IMG_context_priority extension, so
> > > it'll only be about granularity of the scale.
> > > 
> > > I would suggest to go with the nice like scale for easy user adoption,
> > > then just apply that as the N most significant bits.
> > > 
> > > The contexts could then of course further adjust their priority from what
> > > is set by the "gpu_nice" application with the remaining bits.
> > > 
> > > I'm strongly feeling this should be a DRM level "gpu_nice". And the
> > > binding to cgroups should come through DRM core. If it doesn't, limiting
> > > the amount of memory used becomes awkward as the allocation is
> > > centralized to DRM core.
> > > 
> > > > > Also, I might not be up-to-date about all things cgroups, but the way
> > > > > intel_cgroup works, feels bit forced. We create a userspace context just
> > > > > to communicate with the driver and the IOCTL will still have global
> > > > > effects. I can't but think that i915 reading from the cgroups subsystem
> > > > > for the current process would feel more intuitive to me.
> > > > 
> > > > I think you're referring to the earlier discussion about exposing
> > > > priority directly via the cgroups filesystem?  That would certainly be
> > > > simpler from a userspace perspective, but it's not the direction that
> > > > the cgroups maintainer wants to see things go.  Adding files directly to
> > > > the cgroups filesystem is supposed to be something that's reserved for
> > > > official cgroups controllers.  The GPU priority concept we're trying to
> > > > add here doesn't align with the requirements for creating a controller,
> > > > so the preferred approach is to create a custom interface (syscall or
> > > > ioctl) that simply takes a cgroup as a parameter.  There's precendent
> > > > with similar interfaces in areas like BPF (where the bpf() system call
> > > > can accept a cgroup as a parameter and then perform its own private
> > > > policy changes as it sees fit).
> > > > 
> > > > Using a true cgroups controller and exposing settings via the filesystem
> > > > is likely still the way we'll want to go for some other types of
> > > > cgroups-based policy in the future (e.g., limiting GPU memory usage); it
> > > > just isn't the appropriate direction for priority.
> > > 
> > > Might be just me but feels bit crazy to be setting GPU memory usage
> > > through another interface and then doing i915 specific IOCTLs to control
> > > the priority of that same cgroup.
> > > 
> > > I don't feel comfortable adding custom cgroups dependent IOCTLs to i915
> > > where cgroups is only working as the variable carrier in background. We
> > > should really just be consuming a variable from cgroups and it should be
> > > set outside of of the i915 IOCTL interface.
> > > 
> > > I'm still seeing that we should have a DRM cgroups controller and a DRM
> > > subsystem wide application to control the priority and memory usage
> > > to be fed to the drivers.
> > > 
> > > If we end up just supporting i915 apps, we could as well use LD_PRELOAD
> > > wrapper and alter the context priority at creation time for exactly the
> > > same effect and no extra interfaces to maintain.
> > > 
> > > > > Does the implementation mimic some existing cgroups tool or de-facto way
> > > > > of doing things in cgroups world?
> > > > 
> > > > The ioctl approach I took is similar to syscall approach that the BPF
> > > > guys use to attach BPF programs to a cgroup.  I'm not very familiar with
> > > > BPF or how it gets used from userspace, so I'm not sure whether the
> > > > interface is intended for one specific tool (like ours is), or whether
> > > > there's more variety for userspace consumers.
> > > 
> > > Is the proposal to set the memory usage from similar interface, or is
> > > that still not implemented?
> > > 
> > > I'm seeing a very close relation between time-slicing GPU time and
> > > allowed GPU buffer allocations, so having two completely different
> > > interfaces does just feel very hackish way of implementing this.
> > > 
> > > Regards, Joonas
> > > 
> > > > 
> > > > 
> > > > Matt
> > > > 
> > > > > 
> > > > > Regards, Joonas
> > > > > --
> > > > > To unsubscribe from this list: send the line "unsubscribe cgroups" in
> > > > > the body of a message to majordomo at vger.kernel.org
> > > > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > > 
> > > > -- 
> > > > Matt Roper
> > > > Graphics Software Engineer
> > > > IoTG Platform Enabling & Development
> > > > Intel Corporation
> > > > (916) 356-2795
> > --
> > To unsubscribe from this list: send the line "unsubscribe cgroups" in
> > the body of a message to majordomo at vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> -- 
> Matt Roper
> Graphics Software Engineer
> IoTG Platform Enabling & Development
> Intel Corporation
> (916) 356-2795

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795