linux-kernel - Re: [PATCH 5/5] selftests/bpf: a simple benchmark tool for /proc/<pid>/maps APIs

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Message-ID: <CAEf4BzaUgGJVqw_yWOXASHManHQWGQV905Bd-wiaHj-mRob9gw@mail.gmail.com>
Date: Sat, 4 May 2024 14:57:17 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Andrii Nakryiko <andrii@...nel.org>, linux-fsdevel@...r.kernel.org, brauner@...nel.org, 
	viro@...iv.linux.org.uk, akpm@...ux-foundation.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, linux-mm@...ck.org, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, "linux-perf-use." <linux-perf-users@...r.kernel.org>
Subject: Re: [PATCH 5/5] selftests/bpf: a simple benchmark tool for
 /proc/<pid>/maps APIs

On Sat, May 4, 2024 at 8:29 AM Greg KH <gregkh@...uxfoundation.org> 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).

  [0] https://github.com/libbpf/blazesym/blob/ee9b48a80c0b4499118a1e8e5d901cddb2b33ab1/src/normalize/user.rs#L193

> thanks,
>
> greg k-h