Tero Kristo wrote:
Hello,
This patch series adds a new x86 arch specific BPF helper, bpf_rdtsc() which can be used for reading the hardware time stamp counter (TSC.) Currently the same counter is directly accessible from userspace (using RDTSC instruction), and kernel space using various rdtsc_*() APIs, however eBPF lacks the support.
The main usage for the TSC counter is for various profiling and timing purposes, getting accurate cycle counter values. The counter can be currently read from BPF programs by using the existing perf subsystem services (bpf_perf_event_read()), however its usage is cumbersome at best. Additionally, the perf subsystem provides relative value only for the counter, but absolute values are desired by some use cases like Wult [1]. The absolute value of TSC can be read with BPF programs currently via some kprobe / bpf_core_read() magic (see [2], [3], [4] for example), but this relies on accessing kernel internals and is not stable API, and is pretty cumbersome. Thus, this patch proposes a new arch x86 specific BPF helper to avoid the above issues.
-Tero
[1] https://github.com/intel/wult [2] https://github.com/intel/wult/blob/c92237c95b898498faf41e6644983102d1fe5156/... [3] https://github.com/intel/wult/blob/c92237c95b898498faf41e6644983102d1fe5156/... [4] https://github.com/intel/wult/blob/c92237c95b898498faf41e6644983102d1fe5156/...
Makes a lot of sense to me.
Acked-by: John Fastabend john.fastabend@gmail.com