[REPORT] Should rdcycle be deprecated?

[yunhui cui]

Hi All,

1. To use rdcycle in user mode, one must first go through
perf_user_access. However, in reality, the return value of rdcycle
remains unchanged. This is because SBI_PMU_CY_IR_MASK in SBI includes
the bit corresponding to "cycle", and the kernel's pmu_sbi_stop_all()
function disables the counting of cycles.

2. Currently, some application software (e.g., DPDK) uses the rdcycle
instruction. In fact, rdcycle is affected by WFI (Wait for Interrupt)
and CPU frequency variations.

3. Some applications mainly run on server CPUs. Therefore, the
precision design of rdtime should be higher. For example, the TSC
(Time-Stamp Counter) of x86 architectures is generally around 2 GHz,
which can meet the application's requirements for timestamp precision.

4. What are the future plans for rdcycle?

Thanks,
Yunhui