add goal for rustc-perf

Author: davidtwco

src/2025h1/perf-improvements.md

@@ -0,0 +1,113 @@
+# rustc-perf improvements
+
+| Metadata |                                                              |
+| -------- | ------------------------------------------------------------ |
+| Owner(s) | Rust team at Arm, @kobzol                                    |
+| Teams    | [infra], [compiler]                                          |
+| Status   | Proposed                                                     |
+
+*Arm's Rust team is @davidtwco, @adamgemmell, @jacobbramley, @JamieCunliffe and @Jamesbarford.
+This goal will be primarily worked on by @Jamesbarford, but @davidtwco can always be contacted for
+updates.*
+
+## Summary
+
+Add support to rustc-perf for distributed benchmarking across multiple platforms and configuration.
+
+## Motivation
+
+Improving the performance of the Rust compiler is a long-standing objective of the Rust project
+and compiler team, which has led to the development of the project's performance tracking
+infrastructure. While the performance tracking infrastructure has seen many improvements in recent
+years, it cannot scale to support multiple benchmarking machines simultaneously.
+
+There are increasingly demands on the performance infrastructure which require a more scalable
+benchmarking infrastructure - benchmarking the parallel compiler with different thread counts,
+different codegen backends, or different architectures.
+
+### The status quo
+
+rustc-perf does not currently support scheduling and accepting benchmarks from multiple machines,
+requiring a non-trivial rearchitecting to do so. None of our policies around performance triage
+and handling regressions currently consider what to do in case of conflicting benchmarking results.
+
+### The next 6 months
+
+rustc-perf's maintainers have [written a rough draft of the work required to support multiple
+collectors](https://hackmd.io/X1wsQvkwQB-gb5PO7t2Czw) which will form the basis of the work
+completed during this goal. After aligning on a implementation plan with the upstream maintainers
+of rustc-perf and ensuring that the implementation can proceed while placing as little burden on
+the infra team as possible, the work will largely consist of:
+
+1. Establish a parallel testing infrastructure to avoid any disruption to the live rustc-perf
+   service
+2. Plan and implement necessary refactorings to the rustc-perf infrastructure enabling distributed
+   benchmarking
+3. Writing tests for the new distributed rustc-perf infrastructure, enabling future development to
+   avoid breakage
+4. Make changes to the database schema to support receiving results from multiple collectors (both
+   being able to distinguish between results from each configuration and be have multiple writes
+   simultaneously)
+5. Update queries and statistics used in summarising collected performance data and identifying
+   outliers
+6. Update perf.rust-lang.org to be able to display performance data from multiple collectors and
+   make appropriate comparisons (within a configuration, not between configurations)
+
+As this work nears completion, this goal's owners will collaborate with the compiler team and its
+performance working group to extend and update the compiler team's triage and regression handling
+policies. It is important that there are clear guidelines and procedures for circumstances where a
+ benchmark improves on one platform and regresses on another, or how to weigh benchmark results
+from unstable features or configurations (e.g. `-Zthreads=2`) vs the primary benchmarking platforms
+and configurations.
+
+### The "shiny future" we are working towards
+
+Following the completion of this goal, it is anticipated that new platforms and configurations
+will be added to rustc-perf, but this is unlikely to warrant further goals.
+
+## Ownership and team asks
+
+| Subgoal                                        | Owner(s) or team(s)     | Notes |
+| ---------------------------------------------- | ----------------------- | ----- |
+| Discussion and moral support                   | ![Team][] [infra]       |       |
+| Set-up testing infrastructure                  | ![Team][] [infra]       |       |
+| Improve rustc-perf                             |                         |       |
+| ↳ Implementation                               | @Jamesbarford           |       |
+| ↳ Standard reviews                             | ![Team][] [infra]       |       |
+| Deploy rustc-perf improvements                 | ![Team][] [infra]       |       |
+| Update performance regression policy           | ![Team][] [compiler]    |       |
+| ↳ Draft policy and discuss with team           | @davidtwco              |       |
+| Inside Rust blog post announcing improvements  | ![Team][] [infra]       |       |
+
+### Definitions
+
+Definitions for terms used above:
+
+* *Discussion and moral support* is the lowest level offering, basically committing the team to
+  nothing but good vibes and general support for this endeavor.
+* *Author RFC* and *Implementation* means actually writing the code, document, whatever.
+* *Design meeting* means holding a synchronous meeting to review a proposal and provide feedback
+  (no decision expected).
+* *RFC decisions* means reviewing an RFC and deciding whether to accept.
+* *Org decisions* means reaching a decision on an organizational or policy matter.
+* *Secondary review* of an RFC means that the team is "tangentially" involved in the RFC and
+  should be expected to briefly review.
+* *Stabilizations* means reviewing a stabilization and report and deciding whether to stabilize.
+* *Standard reviews* refers to reviews for PRs against the repository; these PRs are not expected
+  to be unduly large or complicated.
+* *Prioritized nominations* refers to prioritized lang-team response to nominated issues, with
+  the expectation that there will be *some* response from the next weekly triage meeting.
+* *Dedicated review* means identifying an individual (or group of individuals) who will review the
+  changes, as they're expected to require significant context.
+* Other kinds of decisions:
+    * [Lang team experiments](https://lang-team.rust-lang.org/how_to/experiment.html) are used
+      to add nightly features that do not yet have an RFC. They are limited to trusted contributors
+      and are used to resolve design details such that an RFC can be written.
+    * Compiler [Major Change Proposal (MCP)](https://forge.rust-lang.org/compiler/mcp.html) is
+      used to propose a 'larger than average' change and get feedback from the compiler team.
+    * Library [API Change Proposal (ACP)](https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html)
+      describes a change to the standard library.
+
+## Frequently asked questions
+
+None yet.