On Wed, Mar 23, 2022 at 01:06:33PM +0100, Bernd Schubert wrote:

On 3/23/22 12:42, Greg KH wrote:

quoted

On Wed, Mar 23, 2022 at 11:26:11AM +0100, Bernd Schubert wrote:

quoted

On 3/23/22 08:16, Greg KH wrote:

quoted

On Tue, Mar 22, 2022 at 08:27:12PM +0100, Miklos Szeredi wrote:

quoted

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 (local)

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