Re: [Xen-devel] [Patch 0 of 2]: PV-domain SMP performance

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 17/12/2008 12:21, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxxxxxxx>
wrote:

> This result was achieved by avoiding descheduling of a vcpu only when irqs
> are blocked. Even better results might be possible with some fine tuning
> (e.g. instrumenting bh_enable/bh_disable).
> I think system time has dropped remarkably!

It's nice, but it'd be more compelling if a win was shown on a real
benchmark. Under normal workloads there is actually little lock contention
in the Linux kernel, and hence I think scope for wins are limited.

Also, pv_ops Linux already has some extra smartness in its spinlock
implementation. A spinner will sleep after some time, making it more likely
that the lock holder will run (who then wakes the sleeper when the lock is
released). You'd need to compare with that approach (which required no extra
hypervisor interfaces).

 -- Keir



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