On Wed, Mar 30, 2022 at 9:34 AM Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > But you are fine with uprobe costs? uprobes appear to be much more costly > > > than a syscall approach on the hardware I've run on. Care to share the numbers? uprobe over USDT is a single trap. Not much slower compared to syscall with kpti. > > > > Can we achieve the same/similar performance with sys_bpf(BPF_PROG_RUN)? > > > > I think so, the tough part is how do you let the user-space know which > program is attached to run? In the current code this is done by the BPF > program attaching to the event via perf and we run the one there if > any when data is emitted out via write calls. > > I would want to make sure that operators can decide where the user-space > data goes (perf/ftrace/eBPF) after the code has been written. With the > current code this is done via the tracepoint callbacks that perf/ftrace > hook up when operators enable recording via perf, tracefs, libbpf, etc. > > We have managed code (C#/Java) where we cannot utilize stubs or traps > easily due to code movement. So we are limited in how we can approach > this problem. Having the interface be mmap/write has enabled this > for us, since it's easy to interact with in most languages and gives us > lifetime management of the trace objects between user-space and the > kernel. Then you should probably invest into making USDT work inside java applications instead of reinventing the wheel. As an alternative you can do a dummy write or any other syscall and attach bpf on the kernel side. No kernel changes are necessary.
