On Wed, Aug 21, 2019 at 06:43:49PM +0000, Yonghong Song wrote: > On 8/21/19 11:31 AM, Peter Zijlstra wrote: > > So extending PERF_RECORD_LOST doesn't work. But PERF_FORMAT_LOST might > > still work fine; but you get to implement it for all software events. > > Could you give more specifics about PERF_FORMAT_LOST? Googling > "PERF_FORMAT_LOST" only yields two emails which we are discussing here :-( Look at what the other PERF_FORMAT_ flags do? Basically it is adding a field to the read(2) output. > >> Maybe we can still use ioctl based approach which is light weighted > >> compared to ring buffer approach? If a fd has bpf attached, nhit/nmisses > >> means the kprobe is processed by bpf program or not. > > > > There is nothing kprobe specific here. Kprobes just appear to be the > > only one actually accounting the recursion cases, but everyone has > > them. > > Sorry to be specific, kprobe is just an example, I actually refers to > any perf event where bpf can attach to, which theoretically are any > perf events which can be opened with "perf_event_open" syscall although > some of them (e.g., software events?) may not have bpf running hooks yet. Yes, BPF is sucky that way.
