linux-kernel - Re: [PATCH bpf-next v2 0/4] Add ftrace direct call for arm64

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Date:   Wed, 5 Oct 2022 17:10:33 +0200
From:   Florent Revest <revest@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Xu Kuohai <xukuohai@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Xu Kuohai <xukuohai@...weicloud.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, Will Deacon <will@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Marc Zyngier <maz@...nel.org>, Guo Ren <guoren@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH bpf-next v2 0/4] Add ftrace direct call for arm64

On Wed, Oct 5, 2022 at 5:07 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, 5 Oct 2022 22:54:15 +0800
> Xu Kuohai <xukuohai@...wei.com> wrote:
>
> > 1.3 attach bpf prog with with direct call, bpftrace -e 'kfunc:vfs_write {}'
> >
> > # dd if=/dev/zero of=/dev/null count=1000000
> > 1000000+0 records in
> > 1000000+0 records out
> > 512000000 bytes (512 MB, 488 MiB) copied, 1.72973 s, 296 MB/s
> >
> >
> > 1.4 attach bpf prog with with indirect call, bpftrace -e 'kfunc:vfs_write {}'
> >
> > # dd if=/dev/zero of=/dev/null count=1000000
> > 1000000+0 records in
> > 1000000+0 records out
> > 512000000 bytes (512 MB, 488 MiB) copied, 1.99179 s, 257 MB/s

Thanks for the measurements Xu!

> Can you show the implementation of the indirect call you used?

Xu used my development branch here
https://github.com/FlorentRevest/linux/commits/fprobe-min-args

As it stands, the performance impact of the fprobe based
implementation would be too high for us. I wonder how much Mark's idea
here https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/ftrace/per-callsite-ops
would help but it doesn't work right now.