riscv64/mmu: cache identity effective-address state#1007
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NEMU Performance Results
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Before this change, get_effective_address() re-derived the same common-case identity mapping from privilege and CSR state on every guest memory access. Most of those inputs only change at MMU or privilege state transitions. After this change, the MMU caches whether data effective-address translation is currently an identity mapping and refreshes that cache only when the relevant state changes. The hot path can now return after a cached boolean check. On linux/coremark-pro with the xs quick-profile flow, this change improved simulation frequency from 532,225,645 instr/s to 550,262,185 instr/s (+3.39%). Workload: ./build/riscv64-nemu-interpreter -b ./workloads/linux/coremark-pro/fw_payload.bin Co-authored-by: Yinan Xu <xuyinan@ict.ac.cn>
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NEMU Performance Results - XS Interpreter
NEMU Performance Results - XS Ref Shared Object
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Before this change, get_effective_address() re-derived the same common-case identity mapping from privilege and CSR state on every guest memory access. Most of those inputs only change at MMU or privilege state transitions.
After this change, the MMU caches whether data effective-address translation is currently an identity mapping and refreshes that cache only when the relevant state changes. The hot path can now return after a cached boolean check.
On linux/coremark-pro with the xs quick-profile flow, this change improved simulation frequency from 532,225,645 instr/s to 550,262,185 instr/s (+3.39%).
Workload: ./build/riscv64-nemu-interpreter -b ./workloads/linux/coremark-pro/fw_payload.bin