Re: How to verify multichannel

["Aurélien Aptel" <aaptel@suse.com>]

Hi Xiaoli,

Xiaoli Feng <xifeng@redhat.com> writes:
> Hello,
>
> When I test multichannel. I don't know how to verify if it works. I just catch network
> packages to see if server and client communicate with multiple IP. But from my test, it
> doesn't. Does any one know how to verify multichannel?

Testing if it works vs checking speed improvement are 2 different
things unfortunately.

Source code
===========

First you need the latest patchset which is available on my github remote:

    https://github.com/aaptel/linux.git

You can use the "multichan-page" branch or you can extract the last
patches of it (with "multichannel:" in the title). These patches add the
multichannel support to the main read/write codepaths from memory pages.

Client setup
============

Then you need to mount with "vers=3.11,multichannel,max_channels=N" where N
will be the total number of channels the client will try to open.

Do a network capture of the mount and run couple of commands in the
mount point (ls, cat, stat, ...).

If the client also has multiple interface, make sure you capture all
interfaces traffic (otherwise you might ignore the other channels).

Interface list check
====================

Look at the trace in wireshark and use "smb2" filter.

Look for "Ioctl Response FSCTL_QUERY_NETWORK_INTERFACE_INFO", if the
server has multiple interfaces you should see a list.

You can also look at /proc/fs/cifs/DebugDate to see the list of
interfaces the client saw and has connected to.

Multichannel check
==================

Still in wireshark:
- right-click on the first "Negotiate protocol" packet
- "Colorize conversation" > "F5 TCP"

You can repeat this for each channel to see clearly different colors for
each channels.

I have made some screenshots, maybe this can help:

https://imgur.com/a/j3IBewF

You can see the alternating colors in my traces that shows different
channels being used.

Speedup check
=============

Now this is the hard part.

If you test with VMs and the interface are "virtual", when you make 2
channels you are actually just dividing by 2 the bandwidth of the
virtual bus, so you won't see much speedup. 

To see a speedup you need to limit the bandwidth of the server
interface, for example 1MB/s to each, so that together with 2 channel
you might see 2MB/s.

You can look into iperf to check raw bandwidth and tc to limit it:
- https://iperf.fr/
- https://netbeez.net/blog/how-to-use-the-linux-traffic-control/

Also similarly if the VM only has 1 CPU you might not see much
improvement as it will switch from one NIC to the other sequentially
instead of in parallel.

This gets tricky very quick...


> Setup:
> server is samba server in linux upstream.
> client is linux upstream.
> smb.conf is:
> [global]
> interfaces = eth1, eth2, team0
> server multi channel support = yes
> vfs objects = recycle aio_pthread
> aio read size = 1
> aio write size = 1
> [cifs]
> path=/mnt/cifs
> writeable=yes

This looks ok but I've mostly used Windows Server 2019 in my test.

Let me know how it goes.

Cheers,
-- 
Aurélien Aptel / SUSE Labs Samba Team
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