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| author | aurel32 <aurelien@aurel32.net> | 2024-01-04 10:16:40 +0100 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2024-01-04 09:16:40 +0000 |
| commit | 99bdb2127d1fa1cff444bbefb814e105c7d20c45 (patch) | |
| tree | f4c178e09dc8cb5a6406f781400d6d5ebcf3dfb8 | |
| parent | e523e454f2866e7dc809c29b0c33ac854c74deb8 (diff) | |
| download | google-benchmark-99bdb2127d1fa1cff444bbefb814e105c7d20c45.tar.gz | |
CycleClock: use RDTIME instead of RDCYCLE on RISC-V (#1727)
Starting with Linux 6.6 [1], RDCYCLE is a privileged instruction on
RISC-V and can't be used directly from userland. There is a sysctl
option to change that as a transition period, but it will eventually
disappear.
Use RDTIME instead, which while less accurate has the advantage of being
synchronized between CPU (and thus monotonic) and of constant frequency.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cc4c07c89aada16229084eeb93895c95b7eabaa3
Co-authored-by: dominic <510002+dmah42@users.noreply.github.com>
| -rw-r--r-- | src/cycleclock.h | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/src/cycleclock.h b/src/cycleclock.h index dfc7ae7..931bba1 100644 --- a/src/cycleclock.h +++ b/src/cycleclock.h @@ -189,15 +189,16 @@ inline BENCHMARK_ALWAYS_INLINE int64_t Now() { #endif return tsc; #elif defined(__riscv) // RISC-V - // Use RDCYCLE (and RDCYCLEH on riscv32) + // Use RDTIME (and RDTIMEH on riscv32). + // RDCYCLE is a privileged instruction since Linux 6.6. #if __riscv_xlen == 32 uint32_t cycles_lo, cycles_hi0, cycles_hi1; // This asm also includes the PowerPC overflow handling strategy, as above. // Implemented in assembly because Clang insisted on branching. asm volatile( - "rdcycleh %0\n" - "rdcycle %1\n" - "rdcycleh %2\n" + "rdtimeh %0\n" + "rdtime %1\n" + "rdtimeh %2\n" "sub %0, %0, %2\n" "seqz %0, %0\n" "sub %0, zero, %0\n" @@ -206,7 +207,7 @@ inline BENCHMARK_ALWAYS_INLINE int64_t Now() { return (static_cast<uint64_t>(cycles_hi1) << 32) | cycles_lo; #else uint64_t cycles; - asm volatile("rdcycle %0" : "=r"(cycles)); + asm volatile("rdtime %0" : "=r"(cycles)); return cycles; #endif #elif defined(__e2k__) || defined(__elbrus__) |