linux-kernel - Re: [PATCH RFC V6 0/11] Paravirtualized ticketlocks

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Date:	Fri, 30 Mar 2012 15:37:42 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Alan Meadows <alan.meadows@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Stephan Diestelhorst <stephan.diestelhorst@....com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Attilio Rao <attilio.rao@...rix.com>
Subject: Re: [PATCH RFC V6 0/11] Paravirtualized ticketlocks

On 03/29/2012 11:33 PM, Raghavendra K T wrote:
> On 03/29/2012 03:28 PM, Avi Kivity wrote:
>> On 03/28/2012 08:21 PM, Raghavendra K T wrote:

> I really like below ideas. Thanks for that!.
>
>> - from the PLE handler, don't wake up a vcpu that is sleeping because it
>> is waiting for a kick
>
> How about, adding another pass in the beginning of kvm_vcpu_on_spin()
> to check if any vcpu is already kicked. This would almost result in
> yield_to(kicked_vcpu). IMO this is also worth trying.
>
> will try above ideas soon.
>

I have patch something like below in mind to try:

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d3b98b1..5127668 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1608,15 +1608,18 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
  	 * else and called schedule in __vcpu_run.  Hopefully that
  	 * VCPU is holding the lock that we need and will release it.
  	 * We approximate round-robin by starting at the last boosted VCPU.
+	 * Priority is given to vcpu that are unhalted.
  	 */
-	for (pass = 0; pass < 2 && !yielded; pass++) {
+	for (pass = 0; pass < 3 && !yielded; pass++) {
  		kvm_for_each_vcpu(i, vcpu, kvm) {
  			struct task_struct *task = NULL;
  			struct pid *pid;
-			if (!pass && i < last_boosted_vcpu) {
+			if (!pass && !vcpu->pv_unhalted)
+				continue;
+			else if (pass == 1 && i < last_boosted_vcpu) {
  				i = last_boosted_vcpu;
  				continue;
-			} else if (pass && i > last_boosted_vcpu)
+			} else if (pass == 2 && i > last_boosted_vcpu)
  				break;
  			if (vcpu == me)
  				continue;

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