envoyproxy/envoy

Make WRR LB thread aware

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#3,278 opened on May 3, 2018

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area/perfenhancementhelp wanted

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Description

The existing WRR LB uses a per-thread EDF scheduler. This makes memory usage O(m * n) where m is the number of hosts and n the number of endpoints. We can shrink this to O(n * w), where w is the weight range, if we precompute the schedule on the main thread (as we do for consistent hash balancers) and just maintain an index that we rotate around the shared schedule for WRR. This comes at the downside of increased memory use when we have a wide range of weights, but as long as we maintain a limited set of weights (which we need to do anyway to sanely support locality weighting with the consistent hash balancers), this should be reasonable.

Contributor guide

Research direction
Understand the current WRR LB implementation using per thread EDF scheduler. Then precompute the schedule on main thread and share it with worker threads, maintaining only an index to rotate. Ensure thread safety and test performance.
Tech stack
cpp
Domain
backendinfrastructureperformance
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C++GitLoad balancing concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25