linux-kernel - [PATCH RFC V3 2/3] kvm: Note down when cpu relax intercepted or pause loop exited

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Message-Id: <20120712191800.30440.16406.sendpatchset@codeblue>
Date:	Fri, 13 Jul 2012 00:48:01 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Avi Kivity <avi@...hat.com>,
	Rik van Riel <riel@...hat.com>
Cc:	S390 <linux-s390@...r.kernel.org>, Carsten Otte <cotte@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	KVM <kvm@...r.kernel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	chegu vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, X86 <x86@...nel.org>,
	Gleb Natapov <gleb@...hat.com>, linux390@...ibm.com,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Joerg Roedel <joerg.roedel@....com>
Subject: [PATCH RFC V3 2/3] kvm: Note down when cpu relax intercepted or pause loop exited

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

Noting pause loop exited or cpu relax intercepted vcpu helps in
filtering right candidate to yield. Wrong selection of vcpu;
i.e., a vcpu that just did a pl-exit or cpu relax intercepted may
contribute to performance degradation.

Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
---
v2 patches were
Reviewed-by: Rik van Riel <riel@...hat.com>

 include/linux/kvm_host.h |   12 ++++++++++++
 virt/kvm/kvm_main.c      |    4 ++++
 2 files changed, 16 insertions(+), 0 deletions(-)


diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c446435..4ec1cf0 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -183,6 +183,18 @@ struct kvm_vcpu {
 	} async_pf;
 #endif
 
+#ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
+	/*
+	 * Cpu relax intercept or pause loop exit optimization
+	 * cpu_relax_intercepted: set when a vcpu does a pause loop exit
+	 *  or cpu relax intercepted.
+	 * dy_eligible: indicates whether vcpu is eligible for directed yield.
+	 */
+	struct {
+		bool cpu_relax_intercepted;
+		bool dy_eligible;
+	} ple;
+#endif
 	struct kvm_vcpu_arch arch;
 };
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7e14068..4ec0120 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -235,6 +235,8 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
 		goto fail;
 	}
 	vcpu->run = page_address(page);
+	vcpu->ple.cpu_relax_intercepted = false;
+	vcpu->ple.dy_eligible = false;
 
 	r = kvm_arch_vcpu_init(vcpu);
 	if (r < 0)
@@ -1577,6 +1579,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
 	int pass;
 	int i;
 
+	me->ple.cpu_relax_intercepted = true;
 	/*
 	 * We boost the priority of a VCPU that is runnable but not
 	 * currently running, because it got preempted by something
@@ -1602,6 +1605,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
 			}
 		}
 	}
+	me->ple.cpu_relax_intercepted = false;
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_on_spin);
 

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