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

From: Scott Wood
Date: Mon Feb 23 2015 - 17:43:58 EST

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]
> Signed-off-by: Bogdan Purcareata <bogdan.purcareata@xxxxxxxxxxxxx>
> Reviewed-by: Scott Wood <scottwood@xxxxxxxxxxxxx>

Where did that Reviewed-by: come from?

A +1 in Gerrit on an internal tree does not translate into an upstream


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