Influence of application priority on IPC

[Norman Feske]

Hello Sergey,

> My use case is quite simple: I tried to start several L4Linux instances and want them to have network available.
> The environment of the use case: Pandaboard, Fiasco.OC (revision 38).
> 
> In order to provide network I use nic_bridge multiplexer which share “Nic” service provided by usb_drv driver. When I set priority of usb_drv to "-1" and priority of nic_bridge to default value, everything works fine. But if I set both priorities to default values, most of L4Linux instances do not obtain IP addresses through DHCP. 
> Also, it was noticed that:
> even in case of obtaining the IP address, after some time of intensive usage of network, the connection becomes unavailable, as well as “Nic” service provided by nic_bridge
> if in the previous case the network is not used intensively, the “ping” detects (from time to time) unreachable network of the L4Linux instance (with obtained IP address)
> 
> According to provided info there is a hypothesis about issue with nic_bridge. As long as this multiplexer plays both client and server roles, the problem occurs when usb_drv tries to get something from nic_bridge. 
> The problem with priority="-1" for usb_drv is that there is a strange delay when closing network connection. Setting both priorities to default value solves this problem, but also creates a bigger one: network is unavailable on most L4Linux instances.

from this description, this looks like a bug lurking somewhere in the
nic_bridge, the L4Linux network stub driver, or usb_drv. At best, the
use of priorities seems to hide a symptom.

Recently, the said components have been reworked quite significantly.
Could you please give your scenario a spin when using the current
genodelabs/master version? This version uses Fiasco.OC rev 40 and
L4Linux rev 25. So please make sure to do a "make prepare" in the
'base-foc' and 'ports-foc' repositories. I also suggest to start with a
clean build directory.

If the problem still persists with the current genodelabs/master branch,
could you provide us with a run script that allows us to reproduce the
scenario?

Best regards
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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