Re: [Xen-devel] [PATCH 39/60] x86: optimize loading of GDT at context switch

[Juergen Gross <jgross@xxxxxxxx>]

On 02.07.19 18:09, Andrew Cooper wrote:
> On 28/05/2019 11:32, Juergen Gross wrote:
> > Instead of dynamically decide whether the previous vcpu was using full
> "deciding"
>
> > or default GDT just add a percpu variable for that purpose. This at
> "was using a full or default GDT, just add"
>
> > once removes the need for testing vcpu_ids to differ twice.
> >
> > Cache the need_full_gdt(nd) value in a local variable.
> What's the point of doing this?  I know the logic is rather complicated
> in __context_switch(), but at least it is visually consistent.  After
> this change, it is asymmetric and harder to follow.
This is a hot path. need_full_gdt() needs two compares, of which one is
using evaluate_nospec().


Juergen

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