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From:   Florent Revest <revest@chromium.org>
Date:   Wed, 5 Oct 2022 17:10:33 +0200
Message-ID: <CABRcYmJGY6fp0CtUBYN8BjEDN=r42BPLSBcrxqu491bTRmfm7g@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 0/4] Add ftrace direct call for arm64
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Xu Kuohai <xukuohai@huawei.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Xu Kuohai <xukuohai@huaweicloud.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        bpf@vger.kernel.org, Will Deacon <will@kernel.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Ingo Molnar <mingo@redhat.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
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On Wed, Oct 5, 2022 at 5:07 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Wed, 5 Oct 2022 22:54:15 +0800
> Xu Kuohai <xukuohai@huawei.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.