linux-kernel - Kconfig help entry for CONFIG_PARAVIRT

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Date:	Tue, 15 Oct 2013 23:45:58 +0200
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	linux-kernel@...r.kernel.org
Subject: Kconfig help entry for CONFIG_PARAVIRT_SPINLOCK

Hi Raghavendra,

Since the ticketlock series have landed in this mergewindow (thanks :-) ) the
help accompanying the Kconfig entry doesn't seem to reflect the current state well.

- Wasn't the whole purpose of the ticketlock series to mitigate this 5% performance hit to something
  far less, so distro kernels could enable this for their normal kernels ?
  I don't have the exact performance figures though.

- Perhaps the suggestion to enable this for supported hypervisors (Xen and KVM ?) could be added ?

--
Sander


CONFIG_PARAVIRT_SPINLOCKS:

Paravirtualized spinlocks allow a pvops backend to replace the
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.

If you are unsure how to answer this question, answer N.

Symbol: PARAVIRT_SPINLOCKS [=y]
Type  : boolean
Prompt: Paravirtualization layer for spinlocks
  Location:
    -> Processor type and features
      -> Linux guest support (HYPERVISOR_GUEST [=y])
        -> Enable paravirtualization code (PARAVIRT [=y])
  Defined at arch/x86/Kconfig:632
  Depends on: HYPERVISOR_GUEST [=y] && PARAVIRT [=y] && SMP [=y]
  Selects: UNINLINE_SPIN_UNLOCK [=y]


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