Re: [Xen-devel] [Patch 2 of 2]: PV-domain SMP performance Linux-part

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 16/01/2009 10:16, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

> I had previously wondered about optimizing spinlocks, my idea was
> basically for Xen to set a bit in a structure to indicate what vcpus are
> currently scheduled, and my modified spinlock acquire routine would
> check if the current vcpu wants a spinlock that is held by a currently
> unscheduled vcpu, and if so yield to Xen to let the other vcpu schedule.

That's a lot more like our existing Linux pv_ops spinlock handling
(yield/block instead of spin) than Juergen's patch (don't deschedule me
while in a critical section). The difference from what you suggest is that
we heuristically detect unscheduled lock holders by spinning a short while.

You can pv up your Windows spinlocks in the block-instead-of-spin way
already (and yield-instead-of-spin is obviously even easier).

 -- Keir



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