On Thu, Aug 8, 2019 at 3:32 PM Daniel Xu <dxu@xxxxxxxxx> wrote: > > On Wed, Aug 7, 2019, at 12:03 PM, Andrii Nakryiko wrote: > > On Tue, Aug 6, 2019 at 4:39 PM Daniel Xu <dxu@xxxxxxxxx> wrote: > > > > > > It's useful to know kprobe's nmissed and nhit stats. For example with > > > > Is nmissed/nhit kprobe-specific? What about tracepoints and raw > > tracepoints, do they have something similar or they can never be > > missed? At least nhit still seems useful, so would be nice to have > > ability to get that with the same API, is it possible? > > > > I'm still trying to grok all the tracepoint/ftrace machinery, but it appears > to me like it is kprobe/uprobe specific. My guess is that b/c tracepoints are > inline (and don't require trapping interrupts), it cannot really "miss". > > This brings up a good point, though. I think we want the same querying > functionality for uprobes so it might be worthwhile to make this API generic. > Something like PERF_EVENT_IOC_QUERY_PROBE so we can later add in > uprobe stats. And maybe tracepoint if it makes sense. > > Thoughts? Yeah, we should definitely unify uprobes, if possible. Having nhit would be great for tracepoints/raw_tracepoints, but we need to look whether it's possible and whether it hurts performance. With bpf_stats we trigger them only from time to time, so counting overhead might be noticeable for some use cases.
