Re: [Xen-devel] switch vcpu on physical cpu

["karim.allah.ahmed@xxxxxxxxx" <karim.allah.ahmed@xxxxxxxxx>]

On Mon, Mar 3, 2014 at 8:10 PM, xennn <openbg@xxxxxx> wrote:
> hello all
>
> I would like to ask about switching vcpu-s on physcial one when we have
> paravirtualization.
>
> I think tha actual switching is happaning at switch_kernel_stack(struct vcpu
> *v) function in domain.c file.
>
>
> static inline void switch_kernel_stack(struct vcpu *v)
> {
>     struct tss_struct *tss = &this_cpu(init_tss);
>     tss->esp1 = v->arch.pv_vcpu.kernel_sp;
>     tss->ss1  = v->arch.pv_vcpu.kernel_ss;
> }
>
> Here the actual task switching is happen - the kernel stack of the current
> physical cpu is get by this_cpu()
> and afther that the kernel stack of that current task is changed to the
> vcpu's one.  So the task is swiched to the new vcpu state.
>
> Is that correct?
>
> I would like to ask what is tss_struct - task structure, task stack segment
> structure or something else?
Hi xennn,

I think TSS here is referring to "Task State Segment". It's an x86
specific feature [0]. If you would like an accurate description, you
can look at IA{32,64} Software Developers Manual [1]

[0] http://en.wikipedia.org/wiki/Task_State_Segment
[1] 
http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html


>
> Best Regards
>
>
>
>
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-- 
Karim Allah Ahmed.

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