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Date:   Fri, 25 Mar 2022 09:54:21 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Karel Zak <kzak@redhat.com>
Cc:     Miklos Szeredi <miklos@szeredi.hu>, Theodore Ts'o <tytso@mit.edu>,
        Christian Brauner <brauner@kernel.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linux API <linux-api@vger.kernel.org>,
        linux-man <linux-man@vger.kernel.org>,
        LSM <linux-security-module@vger.kernel.org>,
        Ian Kent <raven@themaw.net>,
        David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Amir Goldstein <amir73il@gmail.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [RFC PATCH] getvalues(2) prototype
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On Fri, Mar 25, 2022 at 09:46:46AM +0100, Karel Zak wrote:
> On Thu, Mar 24, 2022 at 09:44:38AM +0100, Miklos Szeredi wrote:
> > > If so, have you benchmarked lsof using this new interface?
> > 
> > Not yet.  Looked yesterday at both lsof and procps source code, and
> > both are pretty complex and not easy to plug in a new interface.   But
> > I've not yet given up...
> 
> I can imagine something like getvalues(2) in lsblk (based on /sys) or
> in lsfd (based on /proc; lsof replacement). The tools have defined set
> of information to read from kernel, so gather all the requests to the
> one syscall for each process or block device makes sense and it will
> dramatically reduce number of open+read+close syscalls.

And do those open+read+close syscalls actually show up in measurements?

Again, I tried to find a real-world application that turning those 3
into 1 would matter, and I couldn't.  procps had no decreased system
load that I could notice.  I'll mess with lsof but that's really just a
stress-test, not anything that is run all the time, right?

And as others have said, using io_uring() would also solve the 3 syscall
issue, but no one seems to want to convert these tools to use that,
which implies that it's not really an issue for anyone :)

thanks,

greg k-h