Hi all, I’m currently using Ftrace with tracepoints to trace several events in kernel. But I found the tracing overhead is a little high.
I found the major overhead comes from “local_dec(&cpu_buffer->committing);” in rb_end_commit() function. local_dec() will invoke atomic_long_dec(), which finally performs LOCK_PREFIX plus "DECQ" on this variable. I'm a little confused. cpu_buffer is a per-cpu buffer. Therefore, I cannot come up with a scenario that two core runs INC or DEC on the same per-cpu value at the same time. So, why do we use such heavy-overhead operation here? Can we just simply use "DECQ" without LOCK_PREFIX? Thanks, Tim
