Re: [Xen-devel] Task Switching and Xen-SVM

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 27/10/06 9:59 am, "Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote:

> AMD and Intel are doing the same thing here.
> 
> Do you actually know of any (32-bit) OS that uses task switching? In my
> experience, it's horribly slow (because it generally saves/restores more
> of the context than is necessary). Of course, in 64-bit mode it's not
> even allowed, all task-management features have been removed... I'm
> saying 32-bit OS, since there's probably some 16-bit OS's out there that
> do use task-switching, but those OS's are not able to run on current Xen
> anyways, since Xen in it's current form is very poor at supporting
> segments with base != 0 in protected mode. So far I've only seen a few
> rare reports of anyone actually wishing to run a 16-bit OS...

It's primarily used to obtain a fresh context when things have gobe very bad
(so, for example, double-fault and NMI exceptions often specify a task gate
in the IDT).

 -- Keir



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