Questions about Fiasco.OC scheduler and L4Linux

Marc CHALAND l4 at
Wed Mar 22 16:50:34 CET 2017

Le mer. 22 mars 2017 à 00:59, Adam Lackorzynski <adam at>
a écrit :

On Tue Mar 21, 2017 at 08:31:06 +0100, Marc CHALAND wrote:
> I'm doing a study to port old software on top of Fiasco.OC. This soft uses
> routines which blocks thread scheduling between EnterRegion and
> call. Is there any equivalent on TUDOS ? Did somebody already get this
> challenge ?

Yes, that's what the vCPU model is basically about, i.e. supporting
execution style of an OS. With this you can have EnterRegion and
LeaveRegion by disabling/restoring virtual interrupts.

Is thread scheduling managed by virtual interrupts ? If I disable virtual
IRQ, no other thread will get time slot ?
L4Re documentation about vCPU is very short and I don't understand how it

> I would like to know if L4Linux uses Fiasco.OC scheduler or a user land
> ?

It uses Linux's own scheduler.

So how are scheduled hybrid/alien tasks ? How are the priorities managed
between L4Re threads and L4Linux ones ?

> For our i.MX7d board, Freescale provides Linux drivers on 4.1. I don't
> yet how many drivers we will need. Do you think it is better to port
> drivers from 4.1 to L4Linux 4.3 or later or get a L4Linux 4.1. I have no
> idea about the complexity on doing this.

With a i.MX7d you have hardware support for virtualization, so what
about using that, i.e. running normal Linux in a VM? Getting an L4Linux
for an older version is of course possible but a bit of work.

In that case, is it possible to give hardware access to vm without need to
emulate it ? I've never used this technology yet. I don't know how it works
in L4Re. How are managed the priorities between linux threads and L4Re ones
? Is communication possible between a virtualized linux task and a L4Re
native one ?

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