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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Tue, 31 Mar 2020 21:42:48 +0200
Message-ID: <CAJfpegtn1A=dL9VZJQ2GRWsOiP+YSs-4ezE9YgEYNmb-AF0OLA@mail.gmail.com>
Subject: Re: Upcoming: Notifications, FS notifications and fsinfo()
To:     David Howells <dhowells@redhat.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>, dray@redhat.com,
        Karel Zak <kzak@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Steven Whitehouse <swhiteho@redhat.com>,
        Jeff Layton <jlayton@redhat.com>, Ian Kent <raven@themaw.net>,
        andres@anarazel.de,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Lennart Poettering <mzxreary@0pointer.de>,
        keyrings@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Tue, Mar 31, 2020 at 7:31 PM David Howells <dhowells@redhat.com> wrote:
>
> Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> > The basic problem in my view, is that the performance requirement of a
> > "get filesystem information" type of API just does not warrant a
> > binary coded interface. I've said this a number of times, but it fell
> > on deaf ears.
>
> It hasn't so fallen, but don't necessarily agree with you.  Let's pin some
> numbers on this.

Cool, thanks for testing.  Unfortunately the test-fsinfo-perf.c file
didn't make it into the patch.   Can you please refresh and resend?

> Okay, the results:
>
>   For  1000 mounts, f= 1514us f2= 1102us p=  6014us p2=  6935us; p=4.0*f p=5.5*f2 p=0.9*p2
>   For  2000 mounts, f= 4712us f2= 3675us p= 20937us p2= 22878us; p=4.4*f p=5.7*f2 p=0.9*p2
>   For  3000 mounts, f= 6795us f2= 5304us p= 31080us p2= 34056us; p=4.6*f p=5.9*f2 p=0.9*p2
>   For  4000 mounts, f= 9291us f2= 7434us p= 40723us p2= 46479us; p=4.4*f p=5.5*f2 p=0.9*p2
>   For  5000 mounts, f=11423us f2= 9219us p= 50878us p2= 58857us; p=4.5*f p=5.5*f2 p=0.9*p2
>   For 10000 mounts, f=22899us f2=18240us p=101054us p2=117273us; p=4.4*f p=5.5*f2 p=0.9*p2
>   For 20000 mounts, f=45811us f2=37211us p=203640us p2=237377us; p=4.4*f p=5.5*f2 p=0.9*p2
>   For 30000 mounts, f=69703us f2=54800us p=306778us p2=357629us; p=4.4*f p=5.6*f2 p=0.9*p2

So even the p2 method will give at least 80k queries/s, which is quite
good, considering that the need to rescan the complete mount tree
should be exceedingly rare (and in case it mattered, could be
optimized by priming from /proc/self/mountinfo).

Thanks,
Miklos