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From: Ian Rogers <irogers@google.com>
Date: Sat, 4 May 2024 22:09:39 -0700
Message-ID: <CAP-5=fWPig8-CLLBJ_rb3D6eNAKVY7KX_n_HcpGqL7gfe-=XXg@mail.gmail.com>
Subject: Re: [PATCH 5/5] selftests/bpf: a simple benchmark tool for
 /proc/<pid>/maps APIs
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>, Andrii Nakryiko <andrii@kernel.org>, 
	linux-fsdevel@vger.kernel.org, brauner@kernel.org, viro@zeniv.linux.org.uk, 
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, 
	linux-mm@kvack.org, Arnaldo Carvalho de Melo <acme@kernel.org>, 
	"linux-perf-use." <linux-perf-users@vger.kernel.org>
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On Sat, May 4, 2024 at 2:57=E2=80=AFPM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Sat, May 4, 2024 at 8:29=E2=80=AFAM Greg KH <gregkh@linuxfoundation.or=
g> wrote:
> >
> > On Fri, May 03, 2024 at 05:30:06PM -0700, Andrii Nakryiko wrote:
> > > Implement a simple tool/benchmark for comparing address "resolution"
> > > logic based on textual /proc/<pid>/maps interface and new binary
> > > ioctl-based PROCFS_PROCMAP_QUERY command.
> >
> > Of course an artificial benchmark of "read a whole file" vs. "a tiny
> > ioctl" is going to be different, but step back and show how this is
> > going to be used in the real world overall.  Pounding on this file is
> > not a normal operation, right?
> >
>
> It's not artificial at all. It's *exactly* what, say, blazesym library
> is doing (see [0], it's Rust and part of the overall library API, I
> think C code in this patch is way easier to follow for someone not
> familiar with implementation of blazesym, but both implementations are
> doing exactly the same sequence of steps). You can do it even less
> efficiently by parsing the whole file, building an in-memory lookup
> table, then looking up addresses one by one. But that's even slower
> and more memory-hungry. So I didn't even bother implementing that, it
> would put /proc/<pid>/maps at even more disadvantage.
>
> Other applications that deal with stack traces (including perf) would
> be doing one of those two approaches, depending on circumstances and
> level of sophistication of code (and sensitivity to performance).

The code in perf doing this is here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/too=
ls/perf/util/synthetic-events.c#n440
The code is using the api/io.h code:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/too=
ls/lib/api/io.h
Using perf to profile perf it was observed time was spent allocating
buffers and locale related activities when using stdio, so io is a
lighter weight alternative, albeit with more verbose code than fscanf.
You could add this as an alternate /proc/<pid>/maps reader, we have a
similar benchmark in `perf bench internals synthesize`.

Thanks,
Ian

>   [0] https://github.com/libbpf/blazesym/blob/ee9b48a80c0b4499118a1e8e5d9=
01cddb2b33ab1/src/normalize/user.rs#L193
>
> > thanks,
> >
> > greg k-h
>