linux-kernel - [PATCH] x86 kconfig: Add recommendation to enable paravirt spinlock

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Message-Id: <1382371508-3843-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
Date:	Mon, 21 Oct 2013 21:35:08 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	<mingo@...hat.com>, <hpa@...or.com>, <x86@...nel.org>,
	<gleb@...hat.com>, <pbonzini@...hat.com>, <tglx@...utronix.de>
Cc:	<konrad.wilk@...cle.com>, <linux@...elenboom.it>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Subject: [PATCH] x86 kconfig: Add recommendation to enable paravirt spinlock

Since paravirt spinlock optimization are in 3.12 kernel, we have
very good performance benefit for paravirtualized KVM / Xen kernel.
Also we no longer suffer from 5% side effect on native kernel.

Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
---
 Would like to thank Sander for spotting and suggesting this.
 pvspinlock benefit on KVM link: https://lkml.org/lkml/2013/8/6/178 
 
 Attilio's tests on native kernel impact:
 http://blog.xen.org/index.php/2012/05/11/benchmarking-the-new-pv-ticketlock-implementation/

 arch/x86/Kconfig | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f67e839..4ba9d32 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -638,10 +638,10 @@ config PARAVIRT_SPINLOCKS
 	  spinlock implementation with something virtualization-friendly
 	  (for example, block the virtual CPU rather than spinning).
 
-	  Unfortunately the downside is an up to 5% performance hit on
-	  native kernels, with various workloads.
+	  It has minimal impact on native kernels and gives nice performance
+	  benefit for paravirtualized KVM / Xen kernels.
 
-	  If you are unsure how to answer this question, answer N.
+	  If you are unsure how to answer this question, answer Y.
 
 source "arch/x86/xen/Kconfig"
 
-- 
1.7.11.7

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