[Info-vax] Intel proposal to simplify x86-64

[Dan Cross]

In article <u5qfau$16j37$1 at dont-email.me>,
Simon Clubley  <clubley at remove_me.eisner.decus.org-Earth.UFP> wrote:
>On 2023-06-07, Johnny Billquist <bqt at softjar.se> wrote:
>> On 2023-06-07 14:16, Simon Clubley wrote:
>>> 
>>> QNX.
>>
>> Good point. There are a few more implementations, indeed.
>>
>
>seL4 is also doing some serious stuff with microkernels as well:
>
>https://sel4.systems/
>
>>> We have long moved past the point where absolute speed is the primary
>>> driver in software design. Today, the focus should be on safer computing,
>>> even at the expense of some overhead. To do otherwise is utterly
>>> irresponsible in today's world IMHO.
>>
>> You might think so, and argue for that. Seems most other people are 
>> disagreeing, even to the point of QNX slightly moving away from it for 
>> performance reasons. To quote wikipedia:
>>
>
>That's disappointing. I didn't know that.
>
>Hope that works out better than the time someone decided to move the
>graphics subsystem into the kernel on a certain OS "for performance
>reasons."

Microkernel designs are great for a lot of different reasons,
notably isolation and fault tolerance, but when you have to have
complex protocols between different components, that brings its
own kinds of risk in addition to the obvious performance
degradations.  See some of the sequence diagrams for, say, doing
a read from a file in minix3, for example.  In that kind of
situation, the advantages are far less clear.

But I don't know that this argues against the ukernel approach
so much as for a different division of responsibilities for the
various components.  For example, a hypervisor is a good example
of the type of system where this may make a lot of sense, since
an explicit goal should be to minimize the amount of time one
spends in the HV itself (as otherwise you are stealing cycles
from guests), and one needn't provide general operating system
services like a filesystem or block-storage layer anyway.  The
isolation and fault-tolerance properties are particularly
attractive in that environment, particularly for multi-tenant
scenarios.  E.g, https://hypervisor.org/eurosys2010.pdf

	- Dan C.