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

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Date: Sat, 4 May 2024 17:32:53 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Andrii Nakryiko <andrii@...nel.org>
Cc: 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
Subject: Re: [PATCH 5/5] selftests/bpf: a simple benchmark tool for
 /proc/<pid>/maps APIs

On Fri, May 03, 2024 at 05:30:06PM -0700, Andrii Nakryiko wrote:
> I also did an strace run of both cases. In text-based one the tool did
> 68 read() syscalls, fetching up to 4KB of data in one go.

Why not fetch more at once?

And I have a fun 'readfile()' syscall implementation around here that
needs justification to get merged (I try so every other year or so) that
can do the open/read/close loop in one call, with the buffer size set by
userspace if you really are saying this is a "hot path" that needs that
kind of speedup.  But in the end, io_uring usually is the proper api for
that instead, why not use that here instead of slow open/read/close if
you care about speed?

> In comparison,
> ioctl-based implementation had to do only 6 ioctl() calls to fetch all
> relevant VMAs.
> 
> It is projected that savings from processing big production applications
> would only widen the gap in favor of binary-based querying ioctl API, as
> bigger applications will tend to have even more non-executable VMA
> mappings relative to executable ones.

Define "bigger applications" please.  Is this some "large database
company workload" type of thing, or something else?

thanks,

greg k-h