Re: [Xen-devel] Patch: implementing least priority interrupt routing

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 18/11/08 10:10, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

> Where idle means 'not processing an interrupt'. Which ought to be by far the
> most common case even for a non-idle CPU. Does this really improve load
> balancing all that much? Does BS2000 spend lots of time in IRQ context?
> 
> My fear is that extra complexity here slows down dest_lowprio for all OSes
> (and it's used by a lot of OSes) for every ExtInt delivered.

That fear is probably unfounded actually, given we scan a vcpu's IRR bitmap
on *every* vmentry currently. Still it would be nice to know the motivation
behind this patch (beyond 'it's nice to behave like native hardware'). We
might still find a cheaper method with similar or better benefit (e.g.,
check vcpu_runnable() to find idle VCPUs is cheaper and may be more
accurate).

 -- Keir



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