Subject: Re: [PATCH 1/2] powerpc/kvm: Convert openpic lock to raw_spinlock

From: Scott Wood <[email-masked]>
Date: Mon, 23 Feb 2015 16:43:40 -0600

On Wed, 2015-02-18 at 09:32 +0000, Bogdan Purcareata wrote:
> This patch enables running intensive I/O workloads, e.g. netperf, in a guest
> deployed on a RT host. It also enable guests to be SMP.
> 
> The openpic spinlock becomes a sleeping mutex on a RT system. This no longer
> guarantees that EPR is atomic with exception delivery. The guest VCPU thread
> fails due to a BUG_ON(preemptible()) when running netperf.
> 
> In order to make the kvmppc_mpic_set_epr() call safe on RT from non-atomic
> context, convert the openpic lock to a raw_spinlock. A similar approach can
> be seen for x86 platforms in the following commit [1].
> 
> Here are some comparative cyclitest measurements run inside a high priority RT
> guest run on a RT host. The guest has 1 VCPU and the test has been run for 15
> minutes. The guest runs ~750 hackbench processes as background stress.
> 
>                   spinlock  raw_spinlock
> Min latency (us)  4         4
> Avg latency (us)  15        19
> Max latency (us)  70        62
> 
> [1] https://lkml.org/lkml/2010/1/11/289
> 
> Signed-off-by: Bogdan Purcareata <[email-masked]>
> Reviewed-by: Scott Wood <[email-masked]>

Where did that Reviewed-by: come from?

A +1 in Gerrit on an internal tree does not translate into an upstream
Reviewed-by.

-Scott