On Tue, Dec 19, 2023 at 5:37 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Tue, 19 Dec 2023 14:23:59 +0800 > Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx> wrote: > > > Curious whether it is possible to reuse ftrace's trace buffer instead > > (or it's underlying ring buffer implementation at > > kernel/trace/ring_buffer.c). AFAICT it satisfies both requirements that > > Philo stated: (1) no need for user process as the buffer is accessible > > through tracefs, and (2) has an overwrite mode. > > Yes, the ftrace ring-buffer was in fact designed for the above use case. > > > > > Further more, a natural feature request that would come after > > overwriting support would be snapshotting, and that has already been > > covered in ftrace. > > Yes, it has that too. > > > > > Note: technically BPF program could already write to ftrace's trace > > buffer with the bpf_trace_vprintk() helper, but that goes through string > > formatting and only allows writing into to the global buffer. > > When eBPF was first being developed, Alexei told me he tried the ftrace > ring buffer, and he said the filtering was too slow. That's because it > would always write into the ring buffer and then try to discard it after > the fact, which required a few cmpxchg to synchronize. He decided that the > perf ring buffer was a better fit for this. Well. A lot of things have changed since then :) It might be a good idea to teach bpf to interface with ftrace ring buffers.
