Merge pull request #781 from lmdaly/kep-topology-manager

Topology Manager KEP (Moving to new repo)

Author: k8s-ci-robot

keps/sig-node/0035-20190130-topology-manager.md

@@ -0,0 +1,349 @@
+---
+kep-number: 35
+title: Node Topology Manager
+authors:
+  - "@ConnorDoyle"
+  - "@balajismaniam"
+  - "@lmdaly"
+owning-sig: sig-node
+participating-sigs:
+  - sig-node
+reviewers:
+  - "@vikasc"
+  - "@derekwaynecarr"
+  - "@jeremyeder"
+  - "@RenaudWasTaken"
+approvers:
+  - "@dawnchen"
+  - "@derekwaynecarr"
+editor: Louise Daly
+creation-date: 2019-01-30
+last-updated: 2019-01-30
+status: implementable
+see-also: 
+replaces: 
+superseded-by:
+---
+
+# Node Topology Manager
+
+_Authors:_
+
+* @ConnorDoyle - Connor Doyle <[email protected]>
+* @balajismaniam - Balaji Subramaniam <[email protected]>
+* @lmdaly - Louise M. Daly <[email protected]>
+
+**Contents:**
+
+* [Overview](#overview)
+* [Motivation](#motivation)
+  * [Goals](#goals)
+  * [Non-Goals](#non-goals)
+  * [User Stories](#user-stories)
+* [Proposal](#proposal)
+  * [User Stories](#user-stories)
+  * [Proposed Changes](#proposed-changes)
+    * [New Component: Topology Manager](#new-component-topology-manager)
+      * [Computing Preferred Affinity](#computing-preferred-affinity)
+      * [New Interfaces](#new-interfaces)
+    * [Changes to Existing Components](#changes-to-existing-components)
+* [Graduation Criteria](#graduation-criteria)
+  * [alpha (target v1.11)](#alpha-target-v1.11)
+  * [beta](#beta)
+  * [GA (stable)](#ga-stable)
+* [Challenges](#challenges)
+* [Limitations](#limitations)
+* [Alternatives](#alternatives)
+* [Reference](#reference)
+
+# Overview
+
+An increasing number of systems leverage a combination of CPUs and
+hardware accelerators to support latency-critical execution and
+high-throughput parallel computation. These include workloads in fields
+such as telecommunications, scientific computing, machine learning,
+financial services and data analytics. Such hybrid systems comprise a
+high performance environment.
+
+In order to extract the best performance, optimizations related to CPU
+isolation and memory and device locality are required. However, in
+Kubernetes, these optimizations are handled by a disjoint set of
+components.
+
+This proposal provides a mechanism to coordinate fine-grained hardware
+resource assignments for different components in Kubernetes.
+
+# Motivation
+
+Multiple components in the Kubelet make decisions about system
+topology-related assignments:
+
+- CPU manager
+  - The CPU manager makes decisions about the set of CPUs a container is
+allowed to run on. The only implemented policy as of v1.8 is the static
+one, which does not change assignments for the lifetime of a container.
+- Device manager
+  - The device manager makes concrete device assignments to satisfy
+container resource requirements. Generally devices are attached to one
+peripheral interconnect. If the device manager and the CPU manager are
+misaligned, all communication between the CPU and the device can incur
+an additional hop over the processor interconnect fabric.
+- Container Network Interface (CNI)
+  - NICs including SR-IOV Virtual Functions have affinity to one socket,
+with measurable performance ramifications.
+
+*Related Issues:*
+
+- [Hardware topology awareness at node level (including NUMA)][k8s-issue-49964]
+- [Discover nodes with NUMA architecture][nfd-issue-84]
+- [Support VF interrupt binding to specified CPU][sriov-issue-10]
+- [Proposal: CPU Affinity and NUMA Topology Awareness][proposal-affinity]
+
+Note that all of these concerns pertain only to multi-socket systems. Correct
+behavior requires that the kernel receive accurate topology information from
+the underlying hardware (typically via the SLIT table). See section 5.2.16
+and 5.2.17 of the
+[ACPI Specification](http://www.acpi.info/DOWNLOADS/ACPIspec50.pdf) for more
+information.
+
+## Goals
+
+- Arbitrate preferred socket affinity for containers based on input from
+  CPU manager and Device Manager.
+- Provide an internal interface and pattern to integrate additional
+  topology-aware Kubelet components.
+
+## Non-Goals
+
+- _Inter-device connectivity:_ Decide device assignments based on direct
+  device interconnects. This issue can be separated from socket
+  locality. Inter-device topology can be considered entirely within the
+  scope of the Device Manager, after which it can emit possible
+  socket affinities. The policy to reach that decision can start simple
+  and iterate to include support for arbitrary inter-device graphs.
+- _HugePages:_ This proposal assumes that pre-allocated HugePages are
+  spread among the available memory nodes in the system. We further assume
+  the operating system provides best-effort local page allocation for
+  containers (as long as sufficient HugePages are free on the local memory
+  node.
+- _CNI:_ Changing the Container Networking Interface is out of scope for
+  this proposal. However, this design should be extensible enough to
+  accommodate network interface locality if the CNI adds support in the
+  future. This limitation is potentially mitigated by the possibility to
+  use the device plugin API as a stopgap solution for specialized
+  networking requirements.
+
+## User Stories
+
+*Story 1: Fast virtualized network functions*
+
+A user asks for a "fast network" and automatically gets all the various
+pieces coordinated (hugepages, cpusets, network device) co-located on a
+socket.
+
+*Story 2: Accelerated neural network training*
+
+A user asks for an accelerator device and some number of exclusive CPUs
+in order to get the best training performance, due to socket-alignment of
+the assigned CPUs and devices.
+
+# Proposal
+
+*Main idea: Two phase topology coherence protocol*
+
+Topology affinity is tracked at the container level, similar to devices and
+CPU affinity. At pod admission time, a new component called the Topology
+Manager collects possible configurations from the Device Manager and the
+CPU Manager. The Topology Manager acts as an oracle for local alignment by
+those same components when they make concrete resource allocations. We
+expect the consulted components to use the inferred QoS class of each
+pod in order to prioritize the importance of fulfilling optimal locality.
+
+## Proposed Changes
+
+### New Component: Topology Manager
+
+This proposal is focused on a new component in the Kubelet called the
+Topology Manager. The Topology Manager implements the pod admit handler
+interface and participates in Kubelet pod admission. When the `Admit()`
+function is called, the Topology Manager collects topology hints from other
+Kubelet components.
+
+If the hints are not compatible, the Topology Manager may choose to
+reject the pod. Behavior in this case depends on a new Kubelet configuration
+value to choose the topology policy. The Topology Manager supports two
+modes: `strict` and `preferred` (default). In `strict` mode, the pod is
+rejected if alignment cannot be satisfied. The Topology Manager could
+use `softAdmitHandler` to keep the pod in `Pending` state.
+
+The Topology Manager component will be disabled behind a feature gate until
+graduation from alpha to beta.
+
+#### Computing Preferred Affinity
+
+A topology hint indicates a preference for some well-known local resources.
+Initially, the only supported reference resource is a mask of CPU socket IDs.
+After collecting hints from all providers, the Topology Manager chooses some
+mask that is present in all lists. Here is a sketch:
+
+1. Apply a partial order on each list: number of bits set in the
+   mask, ascending. This biases the result to be more precise if
+   possible.
+1. Iterate over the permutations of preference lists and compute
+   bitwise-and over the masks in each permutation.
+1. Store the first non-empty result and break out early.
+1. If no non-empty result exists, return an error.
+
+The behavior when a match does not exist is configurable, as described
+above.
+
+#### New Interfaces
+
+```go
+package topologymanager
+
+// TopologyManager helps to coordinate local resource alignment
+// within the Kubelet.
+type Manager interface {
+  lifecycle.PodAdmitHandler
+  Store
+  AddHintProvider(HintProvider)
+  RemovePod(podName string)
+}
+
+// SocketMask is a bitmask-like type denoting a subset of available sockets.
+type SocketMask struct{} // TBD
+
+// TopologyHints encodes locality to local resources.
+type TopologyHints struct {
+  Sockets []SocketMask
+}
+
+// HintStore manages state related to the Topology Manager.
+type Store interface {
+  // GetAffinity returns the preferred affinity for the supplied
+  // pod and container.
+  GetAffinity(podName string, containerName string) TopologyHints
+}
+
+// HintProvider is implemented by Kubelet components that make
+// topology-related resource assignments. The Topology Manager consults each
+// hint provider at pod admission time.
+type HintProvider interface {
+  // Returns hints if this hint provider has a preference; otherwise
+  // returns `_, false` to indicate "don't care".
+  GetTopologyHints(pod v1.Pod, containerName string) (TopologyHints, bool)
+}
+```
+
+_Listing: Topology Manager and related interfaces (sketch)._
+
+![topology-manager-components](https://user-images.githubusercontent.com/379372/47447523-8efd2b00-d772-11e8-924d-eea5a5e00037.png)
+
+_Figure: Topology Manager components._
+
+![topology-manager-instantiation](https://user-images.githubusercontent.com/379372/47447526-945a7580-d772-11e8-9761-5213d745e852.png)
+
+_Figure: Topology Manager instantiation and inclusion in pod admit lifecycle._
+
+### Changes to Existing Components
+
+1. Kubelet consults Topology Manager for pod admission (discussed above.)
+1. Add two implementations of Topology Manager interface and a feature gate.
+    1. As much Topology Manager functionality as possible is stubbed when the
+       feature gate is disabled.
+    1. Add a functional Topology Manager that queries hint providers in order
+       to compute a preferred socket mask for each container.
+1. Add `GetTopologyHints()` method to CPU Manager.
+    1. CPU Manager static policy calls `GetAffinity()` method of
+       Topology Manager when deciding CPU affinity.
+1. Add `GetTopologyHints()` method to Device Manager.
+    1. Add Socket ID to Device structure in the device plugin
+       interface. Plugins should be able to determine the socket
+       when enumerating supported devices. See the protocol diff below.
+    1. Device Manager calls `GetAffinity()` method of Topology Manager when
+       deciding device allocation.
+
+```diff
+diff --git a/pkg/kubelet/apis/deviceplugin/v1beta1/api.proto b/pkg/kubelet/apis/deviceplugin/v1beta1/api.proto
+index efbd72c133..f86a1a5512 100644
+--- a/pkg/kubelet/apis/deviceplugin/v1beta1/api.proto
++++ b/pkg/kubelet/apis/deviceplugin/v1beta1/api.proto
+@@ -73,6 +73,10 @@ message ListAndWatchResponse {
+ 	repeated Device devices = 1;
+ }
+
++message TopologyInfo {
++  optional int32 socketID = 1 [default = -1];
++}
++
+ /* E.g:
+ * struct Device {
+ *    ID: "GPU-fef8089b-4820-abfc-e83e-94318197576e",
+@@ -85,6 +89,8 @@ message Device {
+ 	string ID = 1;
+ 	// Health of the device, can be healthy or unhealthy, see constants.go
+ 	string health = 2;
++	// Topology details of the device (optional.)
++	optional TopologyInfo topology = 3;
+ }
+```
+
+_Listing: Amended device plugin gRPC protocol._
+
+![topology-manager-wiring](https://user-images.githubusercontent.com/379372/47447533-9a505680-d772-11e8-95ca-ef9a8290a46a.png)
+
+_Figure: Topology Manager hint provider registration._
+
+![topology-manager-hints](https://user-images.githubusercontent.com/379372/47447543-a0463780-d772-11e8-8412-8bf4a0571513.png)
+
+_Figure: Topology Manager fetches affinity from hint providers._
+
+# Graduation Criteria
+
+## Phase 1: Alpha (target v1.13)
+
+* Feature gate is disabled by default.
+* Alpha-level documentation.
+* Unit test coverage.
+* Node e2e tests.
+* CPU Manager allocation policy takes topology hints into account.
+* Device plugin interface includes socket ID.
+* Device Manager allocation policy takes topology hints into account.
+
+## Phase 2: Beta (later versions)
+
+* Feature gate is enabled by default.
+* Alpha-level documentation.
+* Support hugepages alignment.
+* User feedback.
+
+## GA (stable)
+
+* *TBD*
+
+# Challenges
+
+* Testing the Topology Manager in a continuous integration environment
+  depends on cloud infrastructure to expose multi-node topologies
+  to guest virtual machines.
+* Implementing the `GetHints()` interface may prove challenging.
+
+# Limitations
+
+* *TBD*
+
+# Alternatives
+
+* [AutoNUMA][numa-challenges]: This kernel feature affects memory
+  allocation and thread scheduling, but does not address device locality.
+
+# References
+
+* *TBD*
+
+[k8s-issue-49964]: https://github.com/kubernetes/kubernetes/issues/49964
+[nfd-issue-84]: https://github.com/kubernetes-incubator/node-feature-discovery/issues/84
+[sriov-issue-10]: https://github.com/hustcat/sriov-cni/issues/10
+[proposal-affinity]: https://github.com/kubernetes/community/pull/171
+[numa-challenges]: https://queue.acm.org/detail.cfm?id=2852078