linux-kernel - [PATCH RFC 2/2] kvm: Be courteous to other VMs in overcommitted scenario in PLE handler

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Date:	Fri, 21 Sep 2012 17:30:20 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Avi Kivity <avi@...hat.com>,
	Rik van Riel <riel@...hat.com>
Cc:	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	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>,
	Gleb Natapov <gleb@...hat.com>
Subject: [PATCH RFC 2/2] kvm: Be courteous to other VMs in overcommitted scenario in PLE handler

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

When PLE handler fails to find a better candidate to yield_to, it
goes back and does spin again. This is acceptable when we do not
have overcommit.
But in overcommitted scenarios (especially when we have large
number of small guests), it is better to yield.

Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
---
 virt/kvm/kvm_main.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8323685..713b677 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1660,6 +1660,10 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
 			}
 		}
 	}
+	/* In overcommitted cases, yield instead of spinning */
+	if (!yielded && rq_nr_running() > 1)
+		schedule();
+
 	kvm_vcpu_set_in_spin_loop(me, false);
 
 	/* Ensure vcpu is not eligible during next spinloop */

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