Re: [PATCHv4 bpf-next 0/7] uprobe: uretprobe speed up

[Jiri Olsa]

On Thu, May 02, 2024 at 09:43:02AM -0700, Andrii Nakryiko wrote:
> On Thu, May 2, 2024 at 5:23 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > hi,
> > as part of the effort on speeding up the uprobes [0] coming with
> > return uprobe optimization by using syscall instead of the trap
> > on the uretprobe trampoline.
> >
> > The speed up depends on instruction type that uprobe is installed
> > and depends on specific HW type, please check patch 1 for details.
> >
> > Patches 1-6 are based on bpf-next/master, but path 1 and 2 are
> > apply-able on linux-trace.git tree probes/for-next branch.
> > Patch 7 is based on man-pages master.
> >
> > v4 changes:
> >   - added acks [Oleg,Andrii,Masami]
> >   - reworded the man page and adding more info to NOTE section [Masami]
> >   - rewrote bpf tests not to use trace_pipe [Andrii]
> >   - cc-ed linux-man list
> >
> > Also available at:
> >   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
> >   uretprobe_syscall
> >
> 
> It looks great to me, thanks! Unfortunately BPF CI build is broken,
> probably due to some of the Makefile additions, please investigate and
> fix (or we'll need to fix something on BPF CI side), but it looks like
> you'll need another revision, unfortunately.
> 
> pw-bot: cr
> 
>   [0] https://github.com/kernel-patches/bpf/actions/runs/8923849088/job/24509002194

yes, I think it's missing the 32-bit libc for uprobe_compat binary,
probably it needs to be added to github.com:libbpf/ci.git setup-build-env/action.yml ?
hm but I'm not sure how to test it, need to check

> 
> 
> 
> But while we are at it.
> 
> Masami, Oleg,
> 
> What should be the logistics of landing this? Can/should we route this
> through the bpf-next tree, given there are lots of BPF-based
> selftests? Or you want to take this through
> linux-trace/probes/for-next? In the latter case, it's probably better
> to apply only the first two patches to probes/for-next and the rest
> should still go through the bpf-next tree (otherwise we are running

I think this was the plan, previously mentioned in here:
https://lore.kernel.org/bpf/20240423000943.478ccf1e735a63c6c1b4c66b@xxxxxxxxxx/

> into conflicts in BPF selftests). Previously we were handling such
> cross-tree dependencies by creating a named branch or tag, and merging
> it into bpf-next (so that all SHAs are preserved). It's a bunch of
> extra work for everyone involved, so the simplest way would be to just
> land through bpf-next, of course. But let me know your preferences.
> 
> Thanks!
> 
> > thanks,
> > jirka
> >
> >
> > Notes to check list items in Documentation/process/adding-syscalls.rst:
> >
> > - System Call Alternatives
> >   New syscall seems like the best way in here, becase we need
> 
> typo (thanks, Gmail): because

ok

> 
> >   just to quickly enter kernel with no extra arguments processing,
> >   which we'd need to do if we decided to use another syscall.
> >
> > - Designing the API: Planning for Extension
> >   The uretprobe syscall is very specific and most likely won't be
> >   extended in the future.
> >
> >   At the moment it does not take any arguments and even if it does
> >   in future, it's allowed to be called only from trampoline prepared
> >   by kernel, so there'll be no broken user.
> >
> > - Designing the API: Other Considerations
> >   N/A because uretprobe syscall does not return reference to kernel
> >   object.
> >
> > - Proposing the API
> >   Wiring up of the uretprobe system call si in separate change,
> 
> typo: is

ok, thanks

jirka