On Mon, Oct 26, 2020 at 04:15:48PM -0700, Andrii Nakryiko wrote: > On Sun, Oct 25, 2020 at 12:12 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > On Fri, Oct 23, 2020 at 01:09:26PM -0700, Andrii Nakryiko wrote: > > > On Thu, Oct 22, 2020 at 2:03 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > > > > > Adding trampoline batch attach support so it's possible to use > > > > batch mode to load tracing programs. > > > > > > > > Adding trampoline_attach_batch bool to struct bpf_object_open_opts. > > > > When set to true the bpf_object__attach_skeleton will try to load > > > > all tracing programs via batch mode. > > > > > > > > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> > > > > --- > > > > > > Assuming we go with the current kernel API for batch-attach, why can't > > > libbpf just detect kernel support for it and just use it always, > > > without requiring users to opt into anything? > > > > yea, it's rfc ;-) I wanted some simple usage of the > > interface so it's obvious how it works > > > > if we'll end up with some batch interface I agree > > we should use it as you suggested > > > > > > > > But I'm also confused a bit how this is supposed to be used with BPF > > > skeleton. You use case described in a cover letter (bpftrace glob > > > attach, right?) would have a single BPF program attached to many > > > different functions. While here you are trying to collect different > > > programs and attach each one to its respective kernel function. Do you > > > expect users to have hundreds of BPF programs in their skeletons? If > > > not, I don't really see why adding this complexity. What am I missing? > > > > AFAIU when you use trampoline program you declare the attach point > > at the load time, so you actually can't use same program for different > > kernel functions - which would be great speed up actually, because > > that's where the rest of the cycles in bpftrace is spent (in that cover > > letter example) - load/verifier check of all those programs > > Ah, I see, you are right. And yes, I agree, it would be nice to not > have to clone the BPF program many times to attach to fentry/fexit, if > the program itself doesn't really change. > > > > > it's different for kprobe where you hook single kprobe via multiple > > kprobe perf events to different kernel function > > > > > > > > Now it also seems weird to me for the kernel API to allow attaching > > > many-to-many BPF programs-to-attach points. One BPF program-to-many > > > attach points seems like a more sane and common requirement, no? > > > > right, but that's the consequence of what I wrote above > > Well, maybe we should get rid of that limitation first ;) > I see this as 2 different things.. even when this would be possible - attach single program to multiple trampolines, you still need to install those trampolines via ftrace and you'll end up in this discussion ;-) jirka
