On 03/18, Song Liu wrote: > > > > On Mar 18, 2020, at 1:58 PM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > > > On 3/18/20 7:33 AM, Song Liu wrote: > >>> On Mar 17, 2020, at 4:08 PM, Song Liu <songliubraving@xxxxxx> wrote: > >>>> On Mar 17, 2020, at 2:47 PM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > >>>>>> > >>>>>> Hm, true as well. Wouldn't long-term extending "bpftool prog profile" fentry/fexit > >>>>>> programs supersede this old bpf_stats infrastructure? Iow, can't we implement the > >>>>>> same (or even more elaborate stats aggregation) in BPF via fentry/fexit and then > >>>>>> potentially deprecate bpf_stats counters? > >>>>> I think run_time_ns has its own value as a simple monitoring framework. We can > >>>>> use it in tools like top (and variations). It will be easier for these tools to > >>>>> adopt run_time_ns than using fentry/fexit. > >>>> > >>>> Agree that this is easier; I presume there is no such official integration today > >>>> in tools like top, right, or is there anything planned? > >>> > >>> Yes, we do want more supports in different tools to increase the visibility. > >>> Here is the effort for atop: https://github.com/Atoptool/atop/pull/88 . > >>> > >>> I wasn't pushing push hard on this one mostly because the sysctl interface requires > >>> a user space "owner". > >>> > >>>>> On the other hand, in long term, we may include a few fentry/fexit based programs > >>>>> in the kernel binary (or the rpm), so that these tools can use them easily. At > >>>>> that time, we can fully deprecate run_time_ns. Maybe this is not too far away? > >>>> > >>>> Did you check how feasible it is to have something like `bpftool prog profile top` > >>>> which then enables fentry/fexit for /all/ existing BPF programs in the system? It > >>>> could then sort the sample interval by run_cnt, cycles, cache misses, aggregated > >>>> runtime, etc in a top-like output. Wdyt? > >>> > >>> I wonder whether we can achieve this with one bpf prog (or a trampoline) that covers > >>> all BPF programs, like a trampoline inside __BPF_PROG_RUN()? > >>> > >>> For long term direction, I think we could compare two different approaches: add new > >>> tools (like bpftool prog profile top) vs. add BPF support to existing tools. The > >>> first approach is easier. The latter approach would show BPF information to users > >>> who are not expecting BPF programs in the systems. For many sysadmins, seeing BPF > >>> programs in top/ps, and controlling them via kill is more natural than learning > >>> bpftool. What's your thought on this? > >> More thoughts on this. > >> If we have a special trampoline that attach to all BPF programs at once, we really > >> don't need the run_time_ns stats anymore. Eventually, tools that monitor BPF > >> programs will depend on libbpf, so using fentry/fexit to monitor BPF programs doesn't > >> introduce extra dependency. I guess we also need a way to include BPF program in > >> libbpf. > >> To summarize this plan, we need: > >> 1) A global trampoline that attaches to all BPF programs at once; > > > > Overall sounds good, I think the `at once` part might be tricky, at least it would > > need to patch one prog after another, each prog also needs to store its own metrics > > somewhere for later collection. The start-to-sample could be a shared global var (aka > > shared map between all the programs) which would flip the switch though. > > I was thinking about adding bpf_global_trampoline and use it in __BPF_PROG_RUN. > Something like: > > diff --git i/include/linux/filter.h w/include/linux/filter.h > index 9b5aa5c483cc..ac9497d1fa7b 100644 > --- i/include/linux/filter.h > +++ w/include/linux/filter.h > @@ -559,9 +559,14 @@ struct sk_filter { > > DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key); > > +extern struct bpf_trampoline *bpf_global_trampoline; > +DECLARE_STATIC_KEY_FALSE(bpf_global_tr_active); > + > #define __BPF_PROG_RUN(prog, ctx, dfunc) ({ \ > u32 ret; \ > cant_migrate(); \ > + if (static_branch_unlikely(&bpf_global_tr_active)) \ > + run_the_trampoline(); \ > if (static_branch_unlikely(&bpf_stats_enabled_key)) { \ > struct bpf_prog_stats *stats; \ > u64 start = sched_clock(); \ > > > I am not 100% sure this is OK. > > I am also not sure whether this is an overkill. Do we really want more complex > metric for all BPF programs? Or run_time_ns is enough? I was thinking about exporting a real distribution of the prog runtimes instead of doing an average. It would be interesting to see 50%/95%/99%/max stats.
