Date:	Thu, 4 Dec 2014 16:11:48 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Josh Triplett <josh@...htriplett.org>, laijs@...fujitsu.com
Subject: Re: [PATCH] tinification: Make SRCU optional by using CONFIG_SRCU

On Thu, Dec 04, 2014 at 06:50:24PM -0500, Pranith Kumar wrote:
> SRCU is not necessary to be compiled by default in all cases. For tinification
> efforts not compiling SRCU unless necessary is desirable.
> 
> The current patch tries to make compiling SRCU optional by introducing a new
> Kconfig option CONFIG_SRCU which is selected when any of the components making
> use of SRCU are selected.
> 
> If we do not select CONFIG_SRCU, srcu.o will not be compiled at all.
> 
>    text    data     bss     dec     hex filename
>    2007       0       0    2007     7d7 kernel/rcu/srcu.o
> 
> Size of arch/powerpc/boot/zImage changes from
> 
>    text    data     bss     dec     hex filename
>  831552   64180   23944  919676   e087c arch/powerpc/boot/zImage : before
>  829504   64180   23952  917636   e0084 arch/powerpc/boot/zImage : after
> 
> so the savings are about ~2000 bytes.
> 
> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
> CC: Paul McKenney <paulmck@...ux.vnet.ibm.com>
> CC: Josh Triplett <josh@...htriplett.org>

I have queued this for testing.

Josh, does this look reasonable to you?

Lai, any issues?

							Thanx, Paul

> ---
>  arch/arm/kvm/Kconfig     |  1 +
>  arch/arm64/kvm/Kconfig   |  1 +
>  arch/ia64/kvm/Kconfig    |  1 +
>  arch/mips/kvm/Kconfig    |  1 +
>  arch/powerpc/kvm/Kconfig |  1 +
>  arch/s390/kvm/Kconfig    |  1 +
>  arch/tile/kvm/Kconfig    |  1 +
>  arch/x86/Kconfig         |  1 +
>  arch/x86/kvm/Kconfig     |  1 +
>  drivers/clk/Kconfig      |  1 +
>  drivers/cpufreq/Kconfig  |  1 +
>  drivers/devfreq/Kconfig  |  1 +
>  drivers/md/Kconfig       |  1 +
>  drivers/net/Kconfig      |  1 +
>  fs/btrfs/Kconfig         |  1 +
>  fs/notify/Kconfig        |  1 +
>  init/Kconfig             | 10 ++++++++++
>  kernel/notifier.c        |  3 +++
>  kernel/rcu/Makefile      |  3 ++-
>  lib/Kconfig.debug        |  1 +
>  mm/Kconfig               |  1 +
>  security/tomoyo/Kconfig  |  1 +
>  22 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
> index 466bd29..3afee5f 100644
> --- a/arch/arm/kvm/Kconfig
> +++ b/arch/arm/kvm/Kconfig
> @@ -23,6 +23,7 @@ config KVM
>  	select HAVE_KVM_CPU_RELAX_INTERCEPT
>  	select KVM_MMIO
>  	select KVM_ARM_HOST
> +	select SRCU
>  	depends on ARM_VIRT_EXT && ARM_LPAE
>  	---help---
>  	  Support hosting virtualized guest machines. You will also
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 8ba85e9..b334084 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -26,6 +26,7 @@ config KVM
>  	select KVM_ARM_HOST
>  	select KVM_ARM_VGIC
>  	select KVM_ARM_TIMER
> +	select SRCU
>  	---help---
>  	  Support hosting virtualized guest machines.
> 
> diff --git a/arch/ia64/kvm/Kconfig b/arch/ia64/kvm/Kconfig
> index 3d50ea9..f7d380b 100644
> --- a/arch/ia64/kvm/Kconfig
> +++ b/arch/ia64/kvm/Kconfig
> @@ -29,6 +29,7 @@ config KVM
>  	select HAVE_KVM_IRQ_ROUTING
>  	select KVM_APIC_ARCHITECTURE
>  	select KVM_MMIO
> +	select SRCU
>  	---help---
>  	  Support hosting fully virtualized guest machines using hardware
>  	  virtualization extensions.  You will need a fairly recent
> diff --git a/arch/mips/kvm/Kconfig b/arch/mips/kvm/Kconfig
> index 30e334e..2ae1282 100644
> --- a/arch/mips/kvm/Kconfig
> +++ b/arch/mips/kvm/Kconfig
> @@ -20,6 +20,7 @@ config KVM
>  	select PREEMPT_NOTIFIERS
>  	select ANON_INODES
>  	select KVM_MMIO
> +	select SRCU
>  	---help---
>  	  Support for hosting Guest kernels.
>  	  Currently supported on MIPS32 processors.
> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
> index 602eb51..af18e0f 100644
> --- a/arch/powerpc/kvm/Kconfig
> +++ b/arch/powerpc/kvm/Kconfig
> @@ -21,6 +21,7 @@ config KVM
>  	select PREEMPT_NOTIFIERS
>  	select ANON_INODES
>  	select HAVE_KVM_EVENTFD
> +	select SRCU
> 
>  config KVM_BOOK3S_HANDLER
>  	bool
> diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
> index 646db9c..5fce52c 100644
> --- a/arch/s390/kvm/Kconfig
> +++ b/arch/s390/kvm/Kconfig
> @@ -28,6 +28,7 @@ config KVM
>  	select HAVE_KVM_IRQCHIP
>  	select HAVE_KVM_IRQFD
>  	select HAVE_KVM_IRQ_ROUTING
> +	select SRCU
>  	---help---
>  	  Support hosting paravirtualized guest machines using the SIE
>  	  virtualization capability on the mainframe. This should work
> diff --git a/arch/tile/kvm/Kconfig b/arch/tile/kvm/Kconfig
> index 2298cb1..1e968f7 100644
> --- a/arch/tile/kvm/Kconfig
> +++ b/arch/tile/kvm/Kconfig
> @@ -21,6 +21,7 @@ config KVM
>  	depends on HAVE_KVM && MODULES
>  	select PREEMPT_NOTIFIERS
>  	select ANON_INODES
> +	select SRCU
>  	---help---
>  	  Support hosting paravirtualized guest machines.
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index ded8a67..1c581a0 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -137,6 +137,7 @@ config X86
>  	select HAVE_ACPI_APEI_NMI if ACPI
>  	select ACPI_LEGACY_TABLES_LOOKUP if ACPI
>  	select X86_FEATURE_NAMES if PROC_FS
> +	select SRCU
> 
>  config INSTRUCTION_DECODER
>  	def_bool y
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index f9d16ff..7dc7ba5 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -40,6 +40,7 @@ config KVM
>  	select HAVE_KVM_MSI
>  	select HAVE_KVM_CPU_RELAX_INTERCEPT
>  	select KVM_VFIO
> +	select SRCU
>  	---help---
>  	  Support hosting fully virtualized guest machines using hardware
>  	  virtualization extensions.  You will need a fairly recent
> diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> index 455fd17..53e64f1 100644
> --- a/drivers/clk/Kconfig
> +++ b/drivers/clk/Kconfig
> @@ -13,6 +13,7 @@ config COMMON_CLK
>  	bool
>  	select HAVE_CLK_PREPARE
>  	select CLKDEV_LOOKUP
> +	select SRCU
>  	---help---
>  	  The common clock framework is a single definition of struct
>  	  clk, useful across many platforms, as well as an
> diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
> index 3489f8f..ebaa0cc 100644
> --- a/drivers/cpufreq/Kconfig
> +++ b/drivers/cpufreq/Kconfig
> @@ -2,6 +2,7 @@ menu "CPU Frequency scaling"
> 
>  config CPU_FREQ
>  	bool "CPU Frequency scaling"
> +	select SRCU
>  	help
>  	  CPU Frequency scaling allows you to change the clock speed of 
>  	  CPUs on the fly. This is a nice method to save power, because 
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index faf4e70..3891f67 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -1,5 +1,6 @@
>  menuconfig PM_DEVFREQ
>  	bool "Generic Dynamic Voltage and Frequency Scaling (DVFS) support"
> +	select SRCU
>  	help
>  	  A device may have a list of frequencies and voltages available.
>  	  devfreq, a generic DVFS framework can be registered for a device
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 5bdedf6..c355a22 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -5,6 +5,7 @@
>  menuconfig MD
>  	bool "Multiple devices driver support (RAID and LVM)"
>  	depends on BLOCK
> +	select SRCU
>  	help
>  	  Support multiple physical spindles through a single logical device.
>  	  Required for RAID and logical volume management.
> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> index f9009be..1c7efb1 100644
> --- a/drivers/net/Kconfig
> +++ b/drivers/net/Kconfig
> @@ -177,6 +177,7 @@ config NETCONSOLE_DYNAMIC
> 
>  config NETPOLL
>  	def_bool NETCONSOLE
> +	select SRCU
> 
>  config NET_POLL_CONTROLLER
>  	def_bool NETPOLL
> diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
> index a66768e..80e9c18 100644
> --- a/fs/btrfs/Kconfig
> +++ b/fs/btrfs/Kconfig
> @@ -8,6 +8,7 @@ config BTRFS_FS
>  	select LZO_DECOMPRESS
>  	select RAID6_PQ
>  	select XOR_BLOCKS
> +	select SRCU
> 
>  	help
>  	  Btrfs is a general purpose copy-on-write filesystem with extents,
> diff --git a/fs/notify/Kconfig b/fs/notify/Kconfig
> index 22c629e..2a24249 100644
> --- a/fs/notify/Kconfig
> +++ b/fs/notify/Kconfig
> @@ -1,5 +1,6 @@
>  config FSNOTIFY
>  	def_bool n
> +	select SRCU
> 
>  source "fs/notify/dnotify/Kconfig"
>  source "fs/notify/inotify/Kconfig"
> diff --git a/init/Kconfig b/init/Kconfig
> index 903505e..100f4e7 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -501,9 +501,18 @@ config TINY_RCU
> 
>  endchoice
> 
> +config SRCU
> +	bool "Sleepable form of RCU"
> +	def_bool n
> +	help
> +	  This option selects the sleepable version of RCU. This version
> +	  permits arbitrary sleeping or blocking within RCU read-side critical
> +	  sections.
> +
>  config TASKS_RCU
>  	bool "Task_based RCU implementation using voluntary context switch"
>  	default n
> +	select SRCU
>  	help
>  	  This option enables a task-based RCU implementation that uses
>  	  only voluntary context switch (not preemption!), idle, and
> @@ -1593,6 +1602,7 @@ config PERF_EVENTS
>  	depends on HAVE_PERF_EVENTS
>  	select ANON_INODES
>  	select IRQ_WORK
> +	select SRCU
>  	help
>  	  Enable kernel support for various performance events provided
>  	  by software and hardware.
> diff --git a/kernel/notifier.c b/kernel/notifier.c
> index 4803da6..ae9fc7c 100644
> --- a/kernel/notifier.c
> +++ b/kernel/notifier.c
> @@ -402,6 +402,7 @@ int raw_notifier_call_chain(struct raw_notifier_head *nh,
>  }
>  EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
> 
> +#ifdef CONFIG_SRCU
>  /*
>   *	SRCU notifier chain routines.    Registration and unregistration
>   *	use a mutex, and call_chain is synchronized by SRCU (no locks).
> @@ -528,6 +529,8 @@ void srcu_init_notifier_head(struct srcu_notifier_head *nh)
>  }
>  EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
> 
> +#endif /* CONFIG_SRCU */
> +
>  static ATOMIC_NOTIFIER_HEAD(die_chain);
> 
>  int notrace notify_die(enum die_val val, const char *str,
> diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
> index e6fae50..50a8084 100644
> --- a/kernel/rcu/Makefile
> +++ b/kernel/rcu/Makefile
> @@ -1,4 +1,5 @@
> -obj-y += update.o srcu.o
> +obj-y += update.o
> +obj-$(CONFIG_SRCU) += srcu.o
>  obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
>  obj-$(CONFIG_TREE_RCU) += tree.o
>  obj-$(CONFIG_PREEMPT_RCU) += tree.o
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index d780351..ce76f34 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1199,6 +1199,7 @@ config RCU_TORTURE_TEST
>  	tristate "torture tests for RCU"
>  	depends on DEBUG_KERNEL
>  	select TORTURE_TEST
> +	select SRCU
>  	default n
>  	help
>  	  This option provides a kernel module that runs torture tests
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 1d1ae6b..4395b12 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -325,6 +325,7 @@ config VIRT_TO_BUS
> 
>  config MMU_NOTIFIER
>  	bool
> +	select SRCU
> 
>  config KSM
>  	bool "Enable KSM for page merging"
> diff --git a/security/tomoyo/Kconfig b/security/tomoyo/Kconfig
> index 8eb779b9d..604e718 100644
> --- a/security/tomoyo/Kconfig
> +++ b/security/tomoyo/Kconfig
> @@ -5,6 +5,7 @@ config SECURITY_TOMOYO
>  	select SECURITYFS
>  	select SECURITY_PATH
>  	select SECURITY_NETWORK
> +	select SRCU
>  	default n
>  	help
>  	  This selects TOMOYO Linux, pathname-based access control.
> -- 
> 1.9.1
> 

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