__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.
At the end of the patch set all uses of __get_cpu_var have been removed so
the macro is removed too.
The patch set includes passes over all arches as well. Once these operations
are used throughout then specialized macros can be defined in non -x86
arches as well in order to optimize per cpu access by f.e. using a global
register that may be set to the per cpu base.
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: Richard Henderson <r...@twiddle.net>
CC: Ivan Kokshaysky <i...@jurassic.park.msu.ru>
Cc: Matt Turner <matts...@gmail.com>
Signed-off-by: Christoph Lameter <c...@linux.com>
Index: linux/arch/alpha/kernel/perf_event.c
===================================================================
--- linux.orig/arch/alpha/kernel/perf_event.c 2013-12-02 16:08:01.194316776
-0600
+++ linux/arch/alpha/kernel/perf_event.c 2013-12-02 16:08:01.194316776
-0600
@@ -431,7 +431,7 @@ static void maybe_change_configuration(s
*/
static int alpha_pmu_add(struct perf_event *event, int flags)
{
- struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
int n0;
int ret;
@@ -483,7 +483,7 @@ static int alpha_pmu_add(struct perf_eve
*/
static void alpha_pmu_del(struct perf_event *event, int flags)
{
- struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
unsigned long irq_flags;
int j;
@@ -531,7 +531,7 @@ static void alpha_pmu_read(struct perf_e
static void alpha_pmu_stop(struct perf_event *event, int flags)
{
struct hw_perf_event *hwc = &event->hw;
- struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
if (!(hwc->state & PERF_HES_STOPPED)) {
cpuc->idx_mask &= ~(1UL<<hwc->idx);
@@ -551,7 +551,7 @@ static void alpha_pmu_stop(struct perf_e
static void alpha_pmu_start(struct perf_event *event, int flags)
{
struct hw_perf_event *hwc = &event->hw;
- struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
if (WARN_ON_ONCE(!(hwc->state & PERF_HES_STOPPED)))
return;
@@ -724,7 +724,7 @@ static int alpha_pmu_event_init(struct p
*/
static void alpha_pmu_enable(struct pmu *pmu)
{
- struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
if (cpuc->enabled)
return;
@@ -750,7 +750,7 @@ static void alpha_pmu_enable(struct pmu
static void alpha_pmu_disable(struct pmu *pmu)
{
- struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
if (!cpuc->enabled)
return;
@@ -815,7 +815,7 @@ static void alpha_perf_event_irq_handler
int idx, j;
__this_cpu_inc(irq_pmi_count);
- cpuc = &__get_cpu_var(cpu_hw_events);
+ cpuc = this_cpu_ptr(&cpu_hw_events);
/* Completely counting through the PMC's period to trigger a new PMC
* overflow interrupt while in this interrupt routine is utterly
Index: linux/arch/alpha/kernel/time.c
===================================================================
--- linux.orig/arch/alpha/kernel/time.c 2013-12-02 16:08:01.194316776 -0600
+++ linux/arch/alpha/kernel/time.c 2013-12-02 16:08:01.194316776 -0600
@@ -56,9 +56,9 @@ unsigned long est_cycle_freq;
DEFINE_PER_CPU(u8, irq_work_pending);
-#define set_irq_work_pending_flag() __get_cpu_var(irq_work_pending) = 1
-#define test_irq_work_pending() __get_cpu_var(irq_work_pending)
-#define clear_irq_work_pending() __get_cpu_var(irq_work_pending) = 0
+#define set_irq_work_pending_flag() __this_cpu_write(irq_work_pending, 1)
+#define test_irq_work_pending() __this_cpu_read(irq_work_pending)
+#define clear_irq_work_pending() __this_cpu_writeirq_work_pending, 0)
void arch_irq_work_raise(void)
{
--
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