[Samba] Samba 4.1.6 strange read performance issue.

[Jeremy Allison]

On Fri, Apr 11, 2014 at 03:56:39PM -0700, Hans Rasmussen wrote:
> Hi All
> 
> 
> 
> Having the strangest performance problem with Samba on 1GB ethernet.
> 
> 
> 
> Clients are Windows 7. Server is a modern Xeon on an Intel Board with 16GB
> ram running Opensuse 13.1 with all updates.  Samba is 4.1.6.  smb.conf
> doesn't have anything special in it, haven't played around with the socket
> options.  The server is a Xen host, samba is running on the host, not the
> guest.
> 
> 
> 
> Writes to server are quick, 125MB/sec.  Reads are slow, sometimes starting
> at 11MB/sec, but I have found a strange way of making them go faster.  On
> the server over ssh, I open a 'vim'.  I then hit Ctrl-C to get the escape
> prompt from vim and the read speed instantly doubles, hit it again, the
> speed maxes out at 85MB/sec.  Watching top, the CPU usage by smbd starts at
> 6%, but increases everytime I hit Ctrl-C in vim.  Transferring the same
> file to the server with FTP goes at 125MB/sec both ways.  I'm confused.

TCP tuning ? Get a wireshark trace, only way to be sure..