linux-kernel - Re: [RFC PATCH] getvalues(2) prototype

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Date:   Wed, 23 Mar 2022 13:13:36 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Bernd Schubert <bschubert@....com>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-man@...r.kernel.org,
        linux-security-module@...r.kernel.org, Karel Zak <kzak@...hat.com>,
        Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Dharmendra Singh <dsingh@....com>
Subject: Re: [RFC PATCH] getvalues(2) prototype

On Wed, Mar 23, 2022 at 01:06:33PM +0100, Bernd Schubert wrote:
> 
> 
> On 3/23/22 12:42, Greg KH wrote:
> > On Wed, Mar 23, 2022 at 11:26:11AM +0100, Bernd Schubert wrote:
> > > On 3/23/22 08:16, Greg KH wrote:
> > > > On Tue, Mar 22, 2022 at 08:27:12PM +0100, Miklos Szeredi wrote:
> > > > > Add a new userspace API that allows getting multiple short values in a
> > > > > single syscall.
> > > > > 
> > > > > This would be useful for the following reasons:
> > > > > 
> > > > > - Calling open/read/close for many small files is inefficient.  E.g. on my
> > > > >     desktop invoking lsof(1) results in ~60k open + read + close calls under
> > > > >     /proc and 90% of those are 128 bytes or less.
> > > > 
> > > > As I found out in testing readfile():
> > > > 	https://lore.kernel.org/r/20200704140250.423345-1-gregkh@linuxfoundation.org
> > > > 
> > > > microbenchmarks do show a tiny improvement in doing something like this,
> > > > but that's not a real-world application.
> > > > 
> > > > Do you have anything real that can use this that shows a speedup?
> > > 
> > > Add in network file systems. Demonstrating that this is useful locally and
> > > with micro benchmarks - yeah, helps a bit to make it locally faster. But the
> > > real case is when thousands of clients are handled by a few network servers.
> > > Even reducing wire latency for a single client would make a difference here.
> > 
> > I think I tried running readfile on NFS.  Didn't see any improvements.
> > But please, try it again.  Also note that this proposal isn't for NFS,
> > or any other "real" filesystem :)
> 
> How did you run it on NFS? To get real benefit you would need to add a
> READ_FILE rpc to the NFS protocol and code? Just having it locally won't
> avoid the expensive wire calls?

I did not touch anything related to NFS code, which is perhaps why I did
not notice any difference :)

thanks,

greg k-h