From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> *** vvv Read this first please vvv *** I am re-sending this to dri-devel directly, having realized neither v1 or v2 have reached dri-devel due possible SMTP server issues. Other recipients and lists however did get both v1 in October and v2 two days ago. Hence this is a re-post for the benefit of dri-devel only. And I do understand any replies would create a fork where not all lists, recipients would be up to date with discussions. But I thought dri-devel needed to be made aware of the proposal, while the SMTP server issues are being investigated. Full v1, with some follow up discussion, can be found at these links: https://lists.freedesktop.org/archives/intel-gfx/2022-October/309547.html https://marc.info/?t=166620059900003&r=1&w=4 https://marc.info/?l=linux-cgroups&m=166620044012970&w=2 v2: https://lists.freedesktop.org/archives/intel-gfx/2022-November/311844.html https://marc.info/?l=linux-cgroups&m=166800992215296&w=2 https://marc.info/?l=linux-kernel&m=166800993415302&w=4 *** ^^^ Read this first please ^^^ *** This series contains a proposal for a DRM scheduling cgroup controller which implements a weight based hierarchical GPU usage budget based controller similar in concept to some of the existing controllers. Motivation mostly comes from my earlier proposal where I identified that GPU scheduling lags significantly behind what is available for CPU and IO. Whereas back then I was proposing to somehow tie this with process nice, feedback mostly was that people wanted cgroups. So here it is - in the world of heterogenous computing pipelines I think it is time to do something about this gap. Code is not finished but should survive some light experimenting with. I am sharing it early since the topic has been controversial in the past. I hope to demonstrate there are gains to be had in real world usage(*), today, and that the concepts the proposal relies are well enough established and stable. *) Specifically under ChromeOS which uses cgroups to control CPU bandwith for VMs based on the window focused status. It can be demonstrated how GPU scheduling control can easily be integrated into that setup. There should be no conflict with this proposal and any efforts to implement memory usage based controller. Skeleton DRM cgroup controller is deliberatly purely a skeleton patch where any further functionality can be added with no real conflicts. [In fact, perhaps scheduling is even easier to deal with than memory accounting.] Structure of the series is as follows: 1-3) Improve client ownership tracking in DRM core. 4) Adds a skeleton DRM cgroup controller with no functionality. 5-10) Laying down some infrastructure to enable the controller. 11) The controller itself. 12-13) i915 support for the controller. The proposals defines a delegation of duties between the tree parties: cgroup controller, DRM core and individual drivers. Two way communication interfaces are then defined to enable the delegation to work. DRM scheduling soft limits ~~~~~~~~~~~~~~~~~~~~~~~~~~ Because of the heterogenous hardware and driver DRM capabilities, soft limits are implemented as a loose co-operative (bi-directional) interface between the controller and DRM core. The controller configures the GPU time allowed per group and periodically scans the belonging tasks to detect the over budget condition, at which point it invokes a callback notifying the DRM core of the condition. DRM core provides an API to query per process GPU utilization and 2nd API to receive notification from the cgroup controller when the group enters or exits the over budget condition. Individual DRM drivers which implement the interface are expected to act on this in the best-effort manner only. There are no guarantees that the soft limits will be respected. DRM scheduling soft limits interface files ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drm.weight Standard cgroup weight based control [1, 10000] used to configure the relative distributing of GPU time between the sibling groups. drm.period_us (Most probably only a debugging aid during RFC phase.) An integer representing the period with which the controller should look at the GPU usage by the group and potentially send the over/under budget signal. Value of zero (defaul) disables the soft limit checking. This builds upon the per client GPU utilisation work which landed recently for a few drivers. My thinking is that in principle, an intersect of drivers which support both that and some sort of scheduling control, like priorities, could also in theory support this controller. Another really interesting angle for this controller is that it mimics the same control menthod used by the CPU scheduler. That is the proportional/weight based GPU time budgeting. Which makes it easy to configure and does not need a new mental model. However, as the introduction mentions, GPUs are much more heterogenous and therefore the controller uses very "soft" wording as to what it promises. The general statement is that it can define budgets, notify clients when they are over them, and let individual drivers implement best effort handling of those conditions. Delegation of duties in the implementation goes likes this: * DRM cgroup controller implements the control files and the scanning loop. * DRM core is required to track all DRM clients belonging to processes so it can answer when asked how much GPU time is a process using. * DRM core also provides a call back which the controller will call when a certain process is over budget. * Individual drivers need to implement two similar hooks, but which work for a single DRM client. Over budget callback and GPU utilisation query. What I have demonstrated in practice is that when wired to i915, in a really primitive way where the over-budget condition simply lowers the scheduling priority, the concept can be almost equally effective as the static priority control. I say almost because the design where budget control depends on the periodic usage scanning has a fundamental delay, so responsiveness will depend on the scanning period, which may or may not be a problem for a particular use case. There are also interesting conversations to be had around mental models for what is GPU usage as a single number when faced with GPUs which have different execution engines. To an extent this is similar to the multi-core and cgroup CPU controller problems, but definitely goes further than that. I deliberately did not want to include any such complications in the controller itself and left the individual drivers to handle it. For instance in the i915 over-budget callback it will not do anything unless client's GPU usage is on a physical engine which is oversubscribed. This enables multiple clients to be harmlessly over budget, as long as they are not competing for the same GPU resource. This much for now, hope some good discussion will follow. P.S. A disclaimer of a kind - I was not familiar with how to implement a cgroup controller at all when I started this prototype therefore it is quite possible there are many bugs and misunderstandings on how it should be done. v2: * Prefaced the series with some core DRM work as suggested by Christian. * Dropped the priority based controller for now. * Dropped the introspection cgroup controller file. * Implemented unused budget sharing/propagation. * Some small fixes/tweak as per review feedback and in general. Tvrtko Ursulin (13): drm: Replace DRM_DEBUG with drm_dbg_core in file and ioctl handling drm: Track clients by tgid and not tid drm: Update file owner during use cgroup: Add the DRM cgroup controller drm/cgroup: Track clients per owning process drm/cgroup: Allow safe external access to file_priv drm/cgroup: Add ability to query drm cgroup GPU time drm/cgroup: Add over budget signalling callback drm/cgroup: Only track clients which are providing drm_cgroup_ops cgroup/drm: Client exit hook cgroup/drm: Introduce weight based drm cgroup control drm/i915: Wire up with drm controller GPU time query drm/i915: Implement cgroup controller over budget throttling Documentation/admin-guide/cgroup-v2.rst | 37 ++ drivers/gpu/drm/Kconfig | 1 + drivers/gpu/drm/Makefile | 1 + drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 6 +- drivers/gpu/drm/drm_auth.c | 3 +- drivers/gpu/drm/drm_cgroup.c | 192 ++++++ drivers/gpu/drm/drm_debugfs.c | 12 +- drivers/gpu/drm/drm_file.c | 74 ++- drivers/gpu/drm/drm_ioc32.c | 13 +- drivers/gpu/drm/drm_ioctl.c | 28 +- .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 37 +- drivers/gpu/drm/i915/i915_driver.c | 11 + drivers/gpu/drm/i915/i915_drm_client.c | 169 +++++- drivers/gpu/drm/i915/i915_drm_client.h | 13 + drivers/gpu/drm/nouveau/nouveau_drm.c | 5 +- drivers/gpu/drm/vmwgfx/vmwgfx_gem.c | 6 +- include/drm/drm_clients.h | 47 ++ include/drm/drm_drv.h | 36 ++ include/drm/drm_file.h | 17 +- include/linux/cgroup_drm.h | 13 + include/linux/cgroup_subsys.h | 4 + init/Kconfig | 8 + kernel/cgroup/Makefile | 1 + kernel/cgroup/drm.c | 572 ++++++++++++++++++ 24 files changed, 1249 insertions(+), 57 deletions(-) create mode 100644 drivers/gpu/drm/drm_cgroup.c create mode 100644 include/drm/drm_clients.h create mode 100644 include/linux/cgroup_drm.h create mode 100644 kernel/cgroup/drm.c -- 2.34.1
