Prioritize coprocessor FPU reqs over core FPU reqs #3676
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jerryz123
changed the title
Co-processor reqs will generally be post-commit, from older instructions. Prioritizing these requests avoids deadlock cases.
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But why it will deadlock, I don't understand. It sounds like the deadlock is coming from the structural hazard between scalar and vec/rocc. However they basically has no real dependencies? |
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Suppose a older vector is trying to use the FPU, while the core is trying to execute a younger vector instruction, which needs the FPU at the X stage to access the FP operand. If the younger instruction is given priority, it will read the operand, but then potentially stall+replay at the W stage due to vector unit being busy. Generally, in such a simple pipeline, prioritizing the oldest in-flight operation will avoid deadock conditions. |
sequencer
approved these changes
Sep 8, 2024
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This avoids deadlock conditions due to coprocessor requests typically being from older instructions.
Related issue:
Type of change: bug report | feature request | other enhancement
Impact: no functional change | API addition (no impact on existing code) | API modification
Development Phase: proposal | implementation
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