Re: [Xen-devel] Mini-OS context switching

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

How is it more difficult than context-switching inside the timer interrupt?
In both cases you switch pt_regs and re-enable interrupts. Certainly I don't
think the more complicated way of enabling interrupts makes
context-switching in minios that much more complicated overall.

 -- Keir

On 7/10/07 00:37, "Julian Stecklina" <der_julian@xxxxxx> wrote:

> Hello,
> 
> I am currently trying to implement preemptive multithreading for Mini-OS
> and have the following problem:
> 
> If a context switch needs to occur outside of a timer interrupt, I fail
> to see how to implement it without race condition, because of the
> complex way to enable interrupts (clear memory word and perform a
> hypercall if upcalls are pending). The problem boils down to writing a
> function that takes the new register content as parameter, sets it and
> reenables interrupts. xen.h refers to a HYPERVISOR_stack_switch
> hypercall, which does not seem to be implemented or documented anywhere,
> though.
> 
> In contrast, context switching from an interrupt handler is easy, as it
> just involves changing the struct pt_regs.
> 
> Any help is greatly appreciated, as I am kind of clueless right now.
> 
> Regards,
> Julian
> 
> 
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