Single cpu affinity(UBLK_DEV_F_SINGLE_CPU_AFFINITY)#22
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ming1
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Aug 17, 2025
ming1
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- add feature UBLK_DEV_F_SINGLE_CPU_AFFINITY for just selecting one cpu as queue thread's sched affinity
1. Added new flag to UblkFlags
- enable single CPU affinity optimization: select one random CPU
- from queue's affinity instead of setting all CPUs const
UBLK_DEV_F_SINGLE_CPU_AFFINITY = 0b00010000;
2. Modified create_queue_handlers()
- Added conditional logic to check for the UBLK_DEV_F_SINGLE_CPU_AFFINITY flag
- Only applies random CPU selection and single CPU affinity when the flag is set
- Falls back to original behavior (full affinity) when flag is not set
- Only stores selected CPU information when single CPU mode is enabled
3. Modified build_json()
- Added conditional logic to check for the UBLK_DEV_F_SINGLE_CPU_AFFINITY flag
- Uses stored single CPU affinity when flag is set
- Calls get_queue_affinity() to get full affinity when flag is not set
- Ensures JSON output reflects the actual affinity used by threads
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Test Coverage: 1. Flag Definition and Usage: - Verifies the flag can be combined with other flags using bitwise OR - Tests that flag detection works correctly with contains() 2. Control Device Integration: - Creates devices with and without the flag - Verifies the flag is properly stored and retrieved via get_dev_flags() 3. UblkQueueAffinity Helper Methods: - Tests from_single_cpu() method to create single-CPU affinity - Verifies to_bits_vec() returns correct CPU list - Tests set_cpu() method for building multi-CPU affinity 4. Random CPU Selection: - Creates a multi-CPU affinity (CPUs 1, 3, 5) - Tests get_random_cpu() method returns a valid CPU from the set - Verifies the selection is one of the expected CPUs Test Output: The test produces informative output showing: ✓ Single CPU affinity feature tests passed - Flag definition and usage: PASS - Control device flag storage: PASS - Single CPU affinity creation: PASS - Random CPU selection: PASS (selected CPU 5) Key Benefits: 1. Comprehensive Coverage: Tests both the flag mechanism and the underlying affinity functionality 2. Fast Execution: Doesn't require actual device operation, so it runs quickly 3. Deterministic: Tests concrete functionality rather than relying on system behavior 4. Informative: Provides clear feedback about what was tested and the results The test verifies that: - The new flag is properly defined and can be used - Control devices correctly store and retrieve the flag - Single CPU affinity creation works as expected - Random CPU selection from multi-CPU affinity works correctly Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Function: test_ublk_single_cpu_affinity() What it tests: 1. Device Creation: Creates a ublk device with UBLK_DEV_F_SINGLE_CPU_AFFINITY flag 2. JSON Verification: Reads the exported JSON file and verifies queue affinity configuration 3. Single CPU Constraint: Ensures each queue has exactly one CPU in its affinity 4. Device Functionality: Verifies the device works normally with disk I/O operations Key Features: - Real Integration Test: Actually creates and runs a ublk device, not just unit testing - JSON File Analysis: Reads the real JSON configuration file that ublk exports - Concrete Verification: Checks that each queue's affinity array contains exactly one CPU - Informative Output: Shows which CPU each queue is bound to Test Structure: 1. Flag Setup: Creates device with UblkFlags::UBLK_DEV_F_ADD_DEV | UblkFlags::UBLK_DEV_F_SINGLE_CPU_AFFINITY 2. Device Operation: Runs a functional null device that can handle I/O 3. Verification Functions: - verify_single_cpu_affinity(): Reads JSON and validates affinity - single_cpu_null_handle_queue(): Handles device I/O operations 4. Comprehensive Testing: Runs sanity tests, affinity verification, and I/O tests Benefits: - End-to-End Testing: Tests the complete feature from flag setting to actual CPU binding - Real-World Validation: Uses actual device creation and JSON export mechanisms - Regression Prevention: Ensures the feature continues working as the codebase evolves - Clear Diagnostics: Provides informative output showing actual CPU assignments The test successfully demonstrates that: ✅ Devices can be created with the UBLK_DEV_F_SINGLE_CPU_AFFINITY flag ✅ Each queue gets bound to exactly one CPU (not multiple CPUs) ✅ The feature works with real device operation and I/O handling ✅ The JSON export correctly reflects the single CPU affinity Signed-off-by: Ming Lei <tom.leiming@gmail.com>
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