Re: A small article about the Hurd on L4

[Wolfgang Jährling]

Espen Skoglund <address@hidden> wrote:
> With the current X.2 API you can either 1) implement an interrupt
> distributor thread which forwards the interruption IPC to the
> appropriate drivers and handles the interrupt acking/unmasking,

As we probably want different drivers in different address spaces, this
might be slow.

An extra context switch might be neglible compared to the cost of
manipulating the IRQ controller on IA32, but is this also true for an
ARM with a decent IRQ controller and a fast bus?

> or 2) implement interrupt chaining where you use propagation to hand
> off the interrupt to the next driver in the chain if the current
> driver can not handle the interrupt.  By using propagation the next
> driver in the chain will then be able to do interrupt
> acking/unmasking.

Am I understanding it right that a driver would have to forward it
himself to the next driver?  If so, we rely on the drivers to be
cooperative.  While drivers should be trusted, we still want to minimize
the impact of a buggy driver, and as adding and removing drivers will
require to update the chain, it looks like complexity one might want to
avoid.

Cheers,
GNU/Wolfgang

-- 
Wolfgang Jährling  <address@hidden>  \\  http://stdio.cjb.net/
Debian GNU/Hurd user && Debian GNU/Linux user \\  http://www.gnu.org/
The Hurd Hacking Guide: http://www.gnu.org/software/hurd/hacking-guide/
["We're way ahead of you here. The Hurd has always been on the    ]
[ cutting edge of not being good for anything." -- Roland McGrath ]