> 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? Thanks, Song
