A context switch is only needed if you are changing address spaces.
The kernel does not often have its own address space (although it can).
-Neal
On Wed, Jun 21, 2000 at 09:04:49AM -0700, Jeff Bailey wrote:
> On Tue, Jun 20, 2000 at 05:25:08PM -0400, Olivier Galibert wrote:
>
> > > Now, can't this be done by setting up a direct communication channel
> > > between two userspace processes? With a semaphore you can check on
> > > incoming messages, etc. This way you only need to do a context-switch if
> > > you ask the kernel to set up a direct message-channel.
> >
> > Bzzt wrong. Going userspace->kernel and back does not involve any
> > context switch. It's going userspace->another userspace that does.
>
> Really? I thought I remembered Tanenbaum's book "Modern Operating
> Systems" saying that this was one of the problems with drivers in
> Userspace. It's been a while since I've read it, so I might be wrong. =)
>
> --
> "It is easy to be blinded to the essential uselessness of computers by
> the sense of accomplishment you get from getting them to work at all."
> - Douglas Adams
>
--
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Neal H Walfield [EMAIL PROTECTED]
University of Massachusetts at Lowell [EMAIL PROTECTED]
Fax: 603-415-3645 Phone: N/A (Paris)
Love is the triumph of imagination over intelligence.
-- H. L. Mencken
