feat(BA-4144): Add GlobalDeviceInfo and device discovery infrastructure

[hhoikoo]

resolves #8426 (BA-4144)

Overview

Introduces GlobalDeviceInfo dataclass and device discovery infrastructure to separate device discovery from allocation map creation in ResourceAllocator. This is foundational for the device-based allocation approach in subsequent tickets.

Problem Statement

• Device information was previously intertwined with allocation maps
• No clear separation between discovering what devices exist vs deciding how to allocate them
• The current approach limited flexibility for device-based partitioning strategies

Architecture

flowchart TB
    subgraph "Phase 1: Discovery"
        LP[_load_resources] --> CGD[_create_global_devices]
        CGD --> GDM[GlobalDeviceMap]
    end

    subgraph "Phase 2: Allocation"
        GDM --> CAM[create_alloc_map per plugin]
        CAM --> CC[ComputerContext]
    end

    subgraph "Phase 3: Slots"
        CC --> CTS[_calculate_total_slots]
        CTS --> ATS[available_total_slots]
    end

Loading

The refactored ResourceAllocator.__ainit__() now follows a 3-phase initialization:

1. Device Discovery: _create_global_devices() iterates plugins and calls list_devices()
2. Allocation Maps: Creates ComputerContext with allocation maps from GlobalDeviceInfo
3. Slot Calculation: _calculate_total_slots() uses plugin.available_slots() directly

Key Changes

New Types:

• GlobalDeviceInfo: Dataclass with plugin and devices fields (no alloc_map)
• GlobalDeviceMap: Type alias for Mapping[DeviceName, GlobalDeviceInfo]

New Methods:

• _create_global_devices(): Discovers devices from all plugins, returns GlobalDeviceMap

Refactored Methods:

• __ainit__(): Split into 3 distinct phases with clear separation
• _calculate_total_slots(): Now async, uses plugin.available_slots() directly

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Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

[Copilot]

Pull request overview

This PR introduces GlobalDeviceInfo dataclass and device discovery infrastructure to separate device discovery from allocation map creation in the ResourceAllocator. This refactoring establishes a cleaner 3-phase initialization process and sets the foundation for more flexible device-based allocation strategies.

Changes:

• Added GlobalDeviceInfo dataclass to store plugin references and discovered devices without allocation maps
• Introduced _create_global_devices() method for Phase 1 device discovery across all plugins
• Refactored ResourceAllocator.__ainit__() into 3 distinct phases: device discovery, allocation map creation, and slot calculation
• Made _calculate_total_slots() async to query plugins directly via available_slots() instead of reading from allocation maps

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/ai/backend/agent/resources.py	Introduces GlobalDeviceInfo dataclass, _create_global_devices() method, refactors __ainit__() into 3 phases, and makes _calculate_total_slots() async
tests/unit/agent/test_resources.py	Adds comprehensive unit tests for GlobalDeviceInfo, _create_global_devices(), and the async _calculate_total_slots() method

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[jopemachine]

I think people who are seeing this code for the first time might find it hard to understand what GlobalDevice is. Could you add comments explaining GlobalDevice and how it differs from a non-global Device?

[hhoikoo]

I added some docstring explaining what global device is.