linux/arch/x86
Christoph Lameter 89cbc76768 x86: Replace __get_cpu_var uses
__get_cpu_var() is used for multiple purposes in the kernel source. One of
them is address calculation via the form &__get_cpu_var(x).  This calculates
the address for the instance of the percpu variable of the current processor
based on an offset.

Other use cases are for storing and retrieving data from the current
processors percpu area.  __get_cpu_var() can be used as an lvalue when
writing data or on the right side of an assignment.

__get_cpu_var() is defined as :

#define __get_cpu_var(var) (*this_cpu_ptr(&(var)))

__get_cpu_var() always only does an address determination. However, store
and retrieve operations could use a segment prefix (or global register on
other platforms) to avoid the address calculation.

this_cpu_write() and this_cpu_read() can directly take an offset into a
percpu area and use optimized assembly code to read and write per cpu
variables.

This patch converts __get_cpu_var into either an explicit address
calculation using this_cpu_ptr() or into a use of this_cpu operations that
use the offset.  Thereby address calculations are avoided and less registers
are used when code is generated.

Transformations done to __get_cpu_var()

1. Determine the address of the percpu instance of the current processor.

	DEFINE_PER_CPU(int, y);
	int *x = &__get_cpu_var(y);

    Converts to

	int *x = this_cpu_ptr(&y);

2. Same as #1 but this time an array structure is involved.

	DEFINE_PER_CPU(int, y[20]);
	int *x = __get_cpu_var(y);

    Converts to

	int *x = this_cpu_ptr(y);

3. Retrieve the content of the current processors instance of a per cpu
variable.

	DEFINE_PER_CPU(int, y);
	int x = __get_cpu_var(y)

   Converts to

	int x = __this_cpu_read(y);

4. Retrieve the content of a percpu struct

	DEFINE_PER_CPU(struct mystruct, y);
	struct mystruct x = __get_cpu_var(y);

   Converts to

	memcpy(&x, this_cpu_ptr(&y), sizeof(x));

5. Assignment to a per cpu variable

	DEFINE_PER_CPU(int, y)
	__get_cpu_var(y) = x;

   Converts to

	__this_cpu_write(y, x);

6. Increment/Decrement etc of a per cpu variable

	DEFINE_PER_CPU(int, y);
	__get_cpu_var(y)++

   Converts to

	__this_cpu_inc(y)

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2014-08-26 13:45:49 -04:00
..
boot * Enforce CONFIG_RELOCATABLE for the x86 EFI boot stub, otherwise 2014-08-11 13:58:54 -07:00
configs USB: remove CONFIG_USB_DEBUG from defconfig files 2014-05-28 09:40:45 -07:00
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2014-08-04 09:52:51 -07:00
ia32 x86, vdso: Reimplement vdso.so preparation in build-time C 2014-05-05 13:18:51 -07:00
include x86: Replace __get_cpu_var uses 2014-08-26 13:45:49 -04:00
kernel x86: Replace __get_cpu_var uses 2014-08-26 13:45:49 -04:00
kvm x86: Replace __get_cpu_var uses 2014-08-26 13:45:49 -04:00
lguest asmlinkage, x86: Add explicit __visible to arch/x86/* 2014-05-05 16:07:44 -07:00
lib Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-06-12 19:18:49 -07:00
math-emu asmlinkage, x86: Add explicit __visible to arch/x86/* 2014-05-05 16:07:44 -07:00
mm x86: Replace __get_cpu_var uses 2014-08-26 13:45:49 -04:00
net net: filter: split 'struct sk_filter' into socket and bpf parts 2014-08-02 15:03:58 -07:00
oprofile x86: Replace __get_cpu_var uses 2014-08-26 13:45:49 -04:00
pci Merge branch 'x86-apic-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-08-13 18:23:32 -06:00
platform x86: Replace __get_cpu_var uses 2014-08-26 13:45:49 -04:00
power x86, power, suspend: Annotate restore_processor_state() with notrace 2014-07-17 09:45:05 -04:00
purgatory kexec: support for kexec on panic using new system call 2014-08-08 15:57:33 -07:00
realmode x86/build: Supress realmode.bin is up to date message 2014-04-16 15:17:24 +02:00
syscalls kexec: new syscall kexec_file_load() declaration 2014-08-08 15:57:32 -07:00
tools x86/build: Supress "Nothing to be done for ..." messages 2014-04-14 11:44:36 +02:00
um Merge branch 'signal-cleanup' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/misc 2014-08-09 09:58:12 -07:00
vdso arm64,ia64,ppc,s390,sh,tile,um,x86,mm: remove default gate area 2014-08-08 15:57:27 -07:00
video
xen x86: Replace __get_cpu_var uses 2014-08-26 13:45:49 -04:00
.gitignore
Kbuild purgatory: core purgatory functionality 2014-08-08 15:57:32 -07:00
Kconfig Merge branch 'x86-apic-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-08-13 18:23:32 -06:00
Kconfig.cpu Merge branch 'x86-nuke-platforms-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-04-02 13:15:58 -07:00
Kconfig.debug x86/efi: Dump the EFI page table 2014-03-04 16:17:17 +00:00
Makefile purgatory: core purgatory functionality 2014-08-08 15:57:32 -07:00
Makefile_32.cpu
Makefile.um