linux-kernel - [tip:core/locking] x86/locking/kconfig: Update paravirt spinlock Kconfig description

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Date:	Sat, 26 Oct 2013 06:50:56 -0700
From:	tip-bot for Raghavendra K T <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	konrad.wilk@...cle.com, a.p.zijlstra@...llo.nl,
	torvalds@...ux-foundation.org, gleb@...hat.com,
	raghavendra.kt@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	pbonzini@...hat.com, tglx@...utronix.de, linux@...elenboom.it
Subject: [tip:core/locking] x86/locking/kconfig:
  Update paravirt spinlock Kconfig description

Commit-ID:  4c4e4f61368164f326fe59e2156c70d7faa72c17
Gitweb:     http://git.kernel.org/tip/4c4e4f61368164f326fe59e2156c70d7faa72c17
Author:     Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
AuthorDate: Mon, 21 Oct 2013 21:35:08 +0530
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 26 Oct 2013 12:23:22 +0200

x86/locking/kconfig: Update paravirt spinlock Kconfig description

Since the paravirt spinlock optimizations went into the v3.12 kernel
we have a very good performance benefit for paravirtualized KVM / Xen
kernels. Also we no longer suffer from 5% side effect on native
kernel that is mentioned in the Kconfig entry.

So update the Kconfig entry accordingly.

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/

Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc: <konrad.wilk@...cle.com>
Cc: <linux@...elenboom.it>
Cc: <gleb@...hat.com>
Cc: <pbonzini@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/1382371508-3843-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com
[ Updated the changelog. ]
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/Kconfig | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ee2fb9d..a92572d 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 a minimal impact on native kernels and gives a nice performance
+	  benefit on 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"
 
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