tinification: Introduce CONFIG_SRCU to make SRCU optional

RFC PATCH In review Pranith Kumar 3 participants 6 messages Dec 4, 2014

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Pranith Kumar

author

2014-12-04 04:03 UTC #0 lore raw

RFC PATCH v2 1/1 tinification: Introduce CONFIG_SRCU to make SRCU optional

(CC list trimmed since this is just for initial feedback)

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.

The current tinyconfig on x86 enables SRCU by default since x86 enables PERF_EVENTS which in-turn require SRCU support. If we disable PERF_EVENTS, we can disable compiling SRCU for tiny configs on x86 systems.

I tested this using randconfig and building about 15 kernels. This is definitely not complete and could use more testing. Sticking it in next might help in that regards.

Comments and suggestions are welcome. Please let me know if I should split up this patch.

Signed-off-by Pranith Kumar <[email protected]>

CC Paul McKenney <[email protected]>

CC Josh Triplett <[email protected]>

---
v2:
- handle cpufreq, devfreq and notifier
- build tested tinyconfig on powerpc

 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/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 +
 21 files changed, 33 insertions(+), 1 deletion(-)

arch/arm/kvm/Kconfig +1 -0

index 466bd29..3afee5f 100644
@@ -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

arch/arm64/kvm/Kconfig +1 -0

index 8ba85e9..b334084 100644
@@ -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.

arch/ia64/kvm/Kconfig +1 -0

index 3d50ea9..f7d380b 100644
@@ -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

arch/mips/kvm/Kconfig +1 -0

index 30e334e..2ae1282 100644
@@ -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.

arch/powerpc/kvm/Kconfig +1 -0

index 602eb51..af18e0f 100644
@@ -21,6 +21,7 @@ config KVM
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
 	select HAVE_KVM_EVENTFD
+	select SRCU
 
 config KVM_BOOK3S_HANDLER
 	bool

arch/s390/kvm/Kconfig +1 -0

index 646db9c..5fce52c 100644
@@ -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

arch/tile/kvm/Kconfig +1 -0

index 2298cb1..1e968f7 100644
@@ -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.

arch/x86/kvm/Kconfig +1 -0

index f9d16ff..7dc7ba5 100644
@@ -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

drivers/clk/Kconfig +1 -0

index 455fd17..53e64f1 100644
@@ -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

drivers/cpufreq/Kconfig +1 -0

index 3489f8f..ebaa0cc 100644
@@ -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

drivers/devfreq/Kconfig +1 -0

index faf4e70..3891f67 100644
@@ -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

drivers/md/Kconfig +1 -0

index 5bdedf6..c355a22 100644
@@ -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.

drivers/net/Kconfig +1 -0

index 4706386..221e623 100644
@@ -176,6 +176,7 @@ config NETCONSOLE_DYNAMIC
 
 config NETPOLL
 	def_bool NETCONSOLE
+	select SRCU
 
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL

fs/btrfs/Kconfig +1 -0

index a66768e..80e9c18 100644
@@ -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,

fs/notify/Kconfig +1 -0

index 22c629e..2a24249 100644
@@ -1,5 +1,6 @@
 config FSNOTIFY
 	def_bool n
+	select SRCU
 
 source "fs/notify/dnotify/Kconfig"
 source "fs/notify/inotify/Kconfig"

init/Kconfig +10 -0

index 3ee28ae..80ac0a4 100644
@@ -501,6 +501,14 @@ 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 PREEMPT_RCU
 	def_bool TREE_PREEMPT_RCU
 	help

@@ -510,6 +518,7 @@ config PREEMPT_RCU
 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

@@ -1586,6 +1595,7 @@ 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.

kernel/notifier.c +3 -0

index 4803da6..f52858a 100644
@@ -402,6 +402,7 @@ int raw_notifier_call_chain(struct raw_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
 
+#if 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,

kernel/rcu/Makefile +2 -1

index 807ccfb..a484080 100644
@@ -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_TREE_PREEMPT_RCU) += tree.o

lib/Kconfig.debug +1 -0

index 4e35a5d..797511a 100644
@@ -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

mm/Kconfig +1 -0

index 1d1ae6b..4395b12 100644
@@ -325,6 +325,7 @@ config VIRT_TO_BUS
 
 config MMU_NOTIFIER
 	bool
+	select SRCU
 
 config KSM
 	bool "Enable KSM for page merging"

security/tomoyo/Kconfig +1 -0

index 8eb779b9d..604e718 100644
@@ -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.

Signature · 1 line

1.9.1

Paul E. McKenney

2014-12-04 06:27 UTC #1 lore raw

Quoted 13 lines · Pranith Kumar

(CC list trimmed since this is just for initial feedback)
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.
The current tinyconfig on x86 enables SRCU by default since x86 enables PERF_EVENTS which in-turn require SRCU support. If we disable PERF_EVENTS, we can disable compiling SRCU for tiny configs on x86 systems.

Quoted 6 lines

I tested this using randconfig and building about 15 kernels. This is definitely not complete and could use more testing. Sticking it in next might help in that regards.
Comments and suggestions are welcome. Please let me know if I should split up this patch.

For the moment, I applied this to -rcu against v3.18-rc6 to get some 0day testing on it.

There are conflicts against the tip of my tree, but will worry about that later. I don't have a ready answer on whether or not this needs to be split up -- in the worst case, we would add the SRCU Kconfig parameter, add all the selects, then once they all hit mainline add the Makefile change.

We will need stats on how much memory was saved, and a "size kernel/rcu/srcu.o" after a UP/tiny build should do it. Could you please add this to the commit log?

Josh, and additional thoughts?

Thanx, Paul

Quoted 315 lines

Signed-off-by Pranith Kumar <[email protected]>

CC Paul McKenney <[email protected]>

CC Josh Triplett <[email protected]>

---
v2:
- handle cpufreq, devfreq and notifier
- build tested tinyconfig on powerpc

 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/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 +
 21 files changed, 33 insertions(+), 1 deletion(-)

arch/arm/kvm/Kconfig +1 -0

index 466bd29..3afee5f 100644
@@ -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

arch/arm64/kvm/Kconfig +1 -0

index 8ba85e9..b334084 100644
@@ -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.

arch/ia64/kvm/Kconfig +1 -0

index 3d50ea9..f7d380b 100644
@@ -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

arch/mips/kvm/Kconfig +1 -0

index 30e334e..2ae1282 100644
@@ -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.

arch/powerpc/kvm/Kconfig +1 -0

index 602eb51..af18e0f 100644
@@ -21,6 +21,7 @@ config KVM
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
 	select HAVE_KVM_EVENTFD
+	select SRCU
 
 config KVM_BOOK3S_HANDLER
 	bool

arch/s390/kvm/Kconfig +1 -0

index 646db9c..5fce52c 100644
@@ -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

arch/tile/kvm/Kconfig +1 -0

index 2298cb1..1e968f7 100644
@@ -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.

arch/x86/kvm/Kconfig +1 -0

index f9d16ff..7dc7ba5 100644
@@ -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

drivers/clk/Kconfig +1 -0

index 455fd17..53e64f1 100644
@@ -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

drivers/cpufreq/Kconfig +1 -0

index 3489f8f..ebaa0cc 100644
@@ -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

drivers/devfreq/Kconfig +1 -0

index faf4e70..3891f67 100644
@@ -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

drivers/md/Kconfig +1 -0

index 5bdedf6..c355a22 100644
@@ -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.

drivers/net/Kconfig +1 -0

index 4706386..221e623 100644
@@ -176,6 +176,7 @@ config NETCONSOLE_DYNAMIC
 
 config NETPOLL
 	def_bool NETCONSOLE
+	select SRCU
 
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL

fs/btrfs/Kconfig +1 -0

index a66768e..80e9c18 100644
@@ -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,

fs/notify/Kconfig +1 -0

index 22c629e..2a24249 100644
@@ -1,5 +1,6 @@
 config FSNOTIFY
 	def_bool n
+	select SRCU
 
 source "fs/notify/dnotify/Kconfig"
 source "fs/notify/inotify/Kconfig"

init/Kconfig +10 -0

index 3ee28ae..80ac0a4 100644
@@ -501,6 +501,14 @@ 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 PREEMPT_RCU
 	def_bool TREE_PREEMPT_RCU
 	help

@@ -510,6 +518,7 @@ config PREEMPT_RCU
 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

@@ -1586,6 +1595,7 @@ 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.

kernel/notifier.c +3 -0

index 4803da6..f52858a 100644
@@ -402,6 +402,7 @@ int raw_notifier_call_chain(struct raw_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
 
+#if 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,

kernel/rcu/Makefile +2 -1

index 807ccfb..a484080 100644
@@ -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_TREE_PREEMPT_RCU) += tree.o

lib/Kconfig.debug +1 -0

index 4e35a5d..797511a 100644
@@ -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

mm/Kconfig +1 -0

index 1d1ae6b..4395b12 100644
@@ -325,6 +325,7 @@ config VIRT_TO_BUS
 
 config MMU_NOTIFIER
 	bool
+	select SRCU
 
 config KSM
 	bool "Enable KSM for page merging"

security/tomoyo/Kconfig +1 -0

index 8eb779b9d..604e718 100644
@@ -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.

Signature · 1 line

1.9.1

Pranith Kumar

author

2014-12-04 15:37 UTC #2 lore raw

Quoted 9 lines · Paul E. McKenney

For the moment, I applied this to -rcu against v3.18-rc6 to get some 0day testing on it.
There are conflicts against the tip of my tree, but will worry about that later. I don't have a ready answer on whether or not this needs to be split up -- in the worst case, we would add the SRCU Kconfig parameter, add all the selects, then once they all hit mainline add the Makefile change.

Quoted 4 lines

We will need stats on how much memory was saved, and a "size kernel/rcu/srcu.o" after a UP/tiny build should do it. Could you please add this to the commit log?

So if we do not select CONFIG_SRCU, srcu.o will not be compiled at all. So we should save about

text data bss dec hex filename
2007 0 0 2007 7d7 kernel/rcu/srcu.o

as in 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 about ~2000 bytes I guess.

--
Pranith

Paul E. McKenney

2014-12-04 18:02 UTC #3 lore raw

Quoted 20 lines · Pranith Kumar

Quoted 9 lines · Paul E. McKenney
For the moment, I applied this to -rcu against v3.18-rc6 to get some 0day testing on it.
There are conflicts against the tip of my tree, but will worry about that later. I don't have a ready answer on whether or not this needs to be split up -- in the worst case, we would add the SRCU Kconfig parameter, add all the selects, then once they all hit mainline add the Makefile change.
Quoted 4 lines
We will need stats on how much memory was saved, and a "size kernel/rcu/srcu.o" after a UP/tiny build should do it. Could you please add this to the commit log?
So if we do not select CONFIG_SRCU, srcu.o will not be compiled at all. So we should save about
text data bss dec hex filename
2007 0 0 2007 7d7 kernel/rcu/srcu.o

Quoted 7 lines

as in 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 about ~2000 bytes I guess.

Nice!

Josh, I recall you having a tinified .config somewhere, but don't see it right off. If you do have one, could you please share it with Pranith? Not a big deal, just don't want to overstate the savings too much. ;-)

Thanx, Paul

Josh Triplett

maintainer

2014-12-04 16:13 UTC #4 lore raw

In reply to Pranith Kumar

Quoted 5 lines · Pranith Kumar

(CC list trimmed since this is just for initial feedback)
SRCU is not necessary to be compiled by default in all cases. For tinification efforts not compiling SRCU unless necessary is desirable.

Quoted 7 lines

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.
The current tinyconfig on x86 enables SRCU by default since x86 enables PERF_EVENTS which in-turn require SRCU support. If we disable PERF_EVENTS, we can disable compiling SRCU for tiny configs on x86 systems.

To the best of my knowledge, "select" still doesn't recursively enable things that the selected symbol selects, so I think you need to "select SRCU" from X86, right next to the "select PERF_EVENTS".

Also, can you try your patch on top of the current patch series to compile without perf (tiny/disable-perf), and see if you can successfully compile without SRCU on x86?

Quoted 6 lines

I tested this using randconfig and building about 15 kernels. This is definitely not complete and could use more testing. Sticking it in next might help in that regards.
Comments and suggestions are welcome. Please let me know if I should split up this patch.

I don't think this needs splitting; it's a very small and obvious patch combined with a few selects.

The code looks good to me. Assuming it compiles on x86, with tinyconfig and with allyesconfig minus SRCU (and whatever requires it), this seems reasonable.

Thanks for working on this!

- Josh Triplett

Quoted 311 lines

v2:
- handle cpufreq, devfreq and notifier
- build tested tinyconfig on powerpc

 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/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 +
 21 files changed, 33 insertions(+), 1 deletion(-)

arch/arm/kvm/Kconfig +1 -0

index 466bd29..3afee5f 100644
@@ -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

arch/arm64/kvm/Kconfig +1 -0

index 8ba85e9..b334084 100644
@@ -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.

arch/ia64/kvm/Kconfig +1 -0

index 3d50ea9..f7d380b 100644
@@ -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

arch/mips/kvm/Kconfig +1 -0

index 30e334e..2ae1282 100644
@@ -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.

arch/powerpc/kvm/Kconfig +1 -0

index 602eb51..af18e0f 100644
@@ -21,6 +21,7 @@ config KVM
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
 	select HAVE_KVM_EVENTFD
+	select SRCU
 
 config KVM_BOOK3S_HANDLER
 	bool

arch/s390/kvm/Kconfig +1 -0

index 646db9c..5fce52c 100644
@@ -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

arch/tile/kvm/Kconfig +1 -0

index 2298cb1..1e968f7 100644
@@ -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.

arch/x86/kvm/Kconfig +1 -0

index f9d16ff..7dc7ba5 100644
@@ -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

drivers/clk/Kconfig +1 -0

index 455fd17..53e64f1 100644
@@ -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

drivers/cpufreq/Kconfig +1 -0

index 3489f8f..ebaa0cc 100644
@@ -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

drivers/devfreq/Kconfig +1 -0

index faf4e70..3891f67 100644
@@ -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

drivers/md/Kconfig +1 -0

index 5bdedf6..c355a22 100644
@@ -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.

drivers/net/Kconfig +1 -0

index 4706386..221e623 100644
@@ -176,6 +176,7 @@ config NETCONSOLE_DYNAMIC
 
 config NETPOLL
 	def_bool NETCONSOLE
+	select SRCU
 
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL

fs/btrfs/Kconfig +1 -0

index a66768e..80e9c18 100644
@@ -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,

fs/notify/Kconfig +1 -0

index 22c629e..2a24249 100644
@@ -1,5 +1,6 @@
 config FSNOTIFY
 	def_bool n
+	select SRCU
 
 source "fs/notify/dnotify/Kconfig"
 source "fs/notify/inotify/Kconfig"

init/Kconfig +10 -0

index 3ee28ae..80ac0a4 100644
@@ -501,6 +501,14 @@ 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 PREEMPT_RCU
 	def_bool TREE_PREEMPT_RCU
 	help

@@ -510,6 +518,7 @@ config PREEMPT_RCU
 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

@@ -1586,6 +1595,7 @@ 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.

kernel/notifier.c +3 -0

index 4803da6..f52858a 100644
@@ -402,6 +402,7 @@ int raw_notifier_call_chain(struct raw_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
 
+#if 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,

kernel/rcu/Makefile +2 -1

index 807ccfb..a484080 100644
@@ -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_TREE_PREEMPT_RCU) += tree.o

lib/Kconfig.debug +1 -0

index 4e35a5d..797511a 100644
@@ -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

mm/Kconfig +1 -0

index 1d1ae6b..4395b12 100644
@@ -325,6 +325,7 @@ config VIRT_TO_BUS
 
 config MMU_NOTIFIER
 	bool
+	select SRCU
 
 config KSM
 	bool "Enable KSM for page merging"

security/tomoyo/Kconfig +1 -0

index 8eb779b9d..604e718 100644
@@ -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.

Signature · 1 line

1.9.1

Pranith Kumar

author

2014-12-04 20:27 UTC #5 lore raw

(resending, forgot CC's)

Quoted 8 lines · Josh Triplett

Quoted 4 lines
The current tinyconfig on x86 enables SRCU by default since x86 enables PERF_EVENTS which in-turn require SRCU support. If we disable PERF_EVENTS, we can disable compiling SRCU for tiny configs on x86 systems.
To the best of my knowledge, "select" still doesn't recursively enable things that the selected symbol selects, so I think you need to "select SRCU" from X86, right next to the "select PERF_EVENTS".

Doesn't this prevent not selecting SRCU on x86 systems?

I think a warning will be generated during make if a dependent config is not enabled.

Quoted 4 lines

Also, can you try your patch on top of the current patch series to compile without perf (tiny/disable-perf), and see if you can successfully compile without SRCU on x86?

This branch had a small config error which was compiling perf related code unconditionally.

warning: (HW_BREAKPOINTS) selects HAVE_HW_BREAKPOINT which has unmet direct dependencies (PERF_EVENTS)

With the following patch applied on top of it I was able to compile my patch.

arch/x86/Kconfig +1 -0

index 10c51ff..0ecc069 100644
@@ -588,6 +588,7 @@ config HW_BREAKPOINTS
        default y
        select HAVE_HW_BREAKPOINT
        select HAVE_MIXED_BREAKPOINTS_REGS
+       depends on PERF_EVENTS
        ---help---
          Enable support for x86 hardware breakpoints for debuggers
          and perf.  This will implicitly enable perf-events.

Quoted 5 lines

Quoted 5 lines
I tested this using randconfig and building about 15 kernels. This is definitely not complete and could use more testing. Sticking it in next might help in that regards.

Quoted 8 lines

Quoted 2 lines
Comments and suggestions are welcome. Please let me know if I should split up this patch.
I don't think this needs splitting; it's a very small and obvious patch combined with a few selects.
The code looks good to me. Assuming it compiles on x86, with tinyconfig and with allyesconfig minus SRCU (and whatever requires it), this seems

For allyesconfig minus SRCU(using tiny/disable-perf) I needed the following patch to get it to build

arch/x86/Kconfig +1 -0

index 10c51ff..0ecc069 100644
@@ -588,6 +588,7 @@ config HW_BREAKPOINTS
        default y
        select HAVE_HW_BREAKPOINT
        select HAVE_MIXED_BREAKPOINTS_REGS
+       depends on PERF_EVENTS
        ---help---
          Enable support for x86 hardware breakpoints for debuggers
          and perf.  This will implicitly enable perf-events.

fs/Kconfig.binfmt +1 -0

index 370b24c..2669ddf 100644
@@ -182,6 +182,7 @@ config BINFMT_MISC
 config COREDUMP
        bool "Enable core dump support" if EXPERT
        default y
+       depends on PERF_EVENTS
        help
          This option enables support for performing core dumps. You almost
          certainly want to say Y here. Not necessary on systems that never

kernel/trace/Kconfig +1 -0

index 8639819..b008c597 100644
@@ -125,6 +125,7 @@ config TRACING_SUPPORT
        # irqflags tracing for your architecture.
        depends on TRACE_IRQFLAGS_SUPPORT || PPC32
        depends on STACKTRACE_SUPPORT
+       depends on PERF_EVENTS
        default y
 
 if TRACING_SUPPORT

If the above two patches are good, then may be you should add them to the tiny/disable-perf branch?

I will submit SRCU patch on top of rcu/dev so that Paul can pick it up in his tree.

Thanks!
--
Pranith