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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date: Mon, 6 May 2024 11:32:35 -0700
Message-ID: <CAEf4Bzab+sRQ8pzNYxh1BOgjhDF4yCkqcHxy5YZAyT-jef7Acw@mail.gmail.com>
Subject: Re: [PATCH 5/5] selftests/bpf: a simple benchmark tool for
 /proc/<pid>/maps APIs
To: Ian Rogers <irogers@google.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 10:09=E2=80=AFPM Ian Rogers <irogers@google.com> wro=
te:
>
> 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.=
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).
>
> The code in perf doing this is here:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/t=
ools/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/t=
ools/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`.
>

If I add a new implementation using this ioctl() into
perf_event__synthesize_mmap_events(), will it be tested from this
`perf bench internals synthesize`? I'm not too familiar with perf code
organization, sorry if it's a stupid question. If not, where exactly
is the code that would be triggered from benchmark?

> Thanks,
> Ian
>
> >   [0] https://github.com/libbpf/blazesym/blob/ee9b48a80c0b4499118a1e8e5=
d901cddb2b33ab1/src/normalize/user.rs#L193
> >
> > > thanks,
> > >
> > > greg k-h
> >