linux-kernel - [PATCH RFC 2/2] kvm: Iterate over only vcpus that are preempted

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Message-Id: <20130304180227.31281.96284.sendpatchset@codeblue.in.ibm.com>
Date:	Mon, 04 Mar 2013 23:32:27 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Avi Kivity <avi.kivity@...il.com>,
	Gleb Natapov <gleb@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Rik van Riel <riel@...hat.com>
Cc:	Srikar <srikar@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiannan Ouyang <ouyang@...pitt.edu>,
	Chegu Vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Andrew Jones <drjones@...hat.com>
Subject: [PATCH RFC 2/2] kvm: Iterate over only vcpus that are preempted

From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>

This helps in filtering out the eligible candidates further and 
thus potentially helps in quickly allowing preempted lockholders to run.
Note that if a vcpu was spinning during preemption we filter them
by checking whether they are preempted due to pause loop exit.

Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
---
 virt/kvm/kvm_main.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 83a804c..60114e1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1790,6 +1790,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
 				continue;
 			} else if (pass && i > last_boosted_vcpu)
 				break;
+			if (!ACCESS_ONCE(vcpu->preempted))
+				continue;
 			if (vcpu == me)
 				continue;
 			if (waitqueue_active(&vcpu->wq))

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