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Date: Sat, 31 Aug 2013 13:36:00 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Christoph Lameter <cl@...ux.com>
Cc: Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
Dipankar Sarma <dipankar@...ibm.com>,
linux-arch@...r.kernel.org, Steven Rostedt <srostedt@...hat.com>,
linux-kernel@...r.kernel.org
Subject: Re: [gcv v3 10/35] rcu: Replace __get_cpu_var uses
On Wed, Aug 28, 2013 at 07:48:17PM +0000, Christoph Lameter wrote:
> __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 calcualtions are avoided
> and less registers are used when code is generated.
>
> At the end of the patchset all uses of __get_cpu_var have been removed so the macro is removed too.
>
> The patchset 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, u);
> 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(this_cpu_ptr(&x), 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)
>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
Queued for 3.13. I had to rework for conflicts, please see below for
the update patch.
Thanx, Paul
------------------------------------------------------------------------
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index a51985e..fccb6e8 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -400,7 +400,7 @@ static void rcu_eqs_enter(bool user)
long long oldval;
struct rcu_dynticks *rdtp;
- rdtp = &__get_cpu_var(rcu_dynticks);
+ rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
@@ -428,7 +428,7 @@ void rcu_idle_enter(void)
local_irq_save(flags);
rcu_eqs_enter(false);
- rcu_sysidle_enter(&__get_cpu_var(rcu_dynticks), 0);
+ rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks), 0);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);
@@ -471,7 +471,7 @@ void rcu_irq_exit(void)
struct rcu_dynticks *rdtp;
local_irq_save(flags);
- rdtp = &__get_cpu_var(rcu_dynticks);
+ rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting--;
WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
@@ -521,7 +521,7 @@ static void rcu_eqs_exit(bool user)
struct rcu_dynticks *rdtp;
long long oldval;
- rdtp = &__get_cpu_var(rcu_dynticks);
+ rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
WARN_ON_ONCE(oldval < 0);
if (oldval & DYNTICK_TASK_NEST_MASK)
@@ -548,7 +548,7 @@ void rcu_idle_exit(void)
local_irq_save(flags);
rcu_eqs_exit(false);
- rcu_sysidle_exit(&__get_cpu_var(rcu_dynticks), 0);
+ rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks), 0);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);
@@ -592,7 +592,7 @@ void rcu_irq_enter(void)
long long oldval;
local_irq_save(flags);
- rdtp = &__get_cpu_var(rcu_dynticks);
+ rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting++;
WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
@@ -613,7 +613,7 @@ void rcu_irq_enter(void)
*/
void rcu_nmi_enter(void)
{
- struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
if (rdtp->dynticks_nmi_nesting == 0 &&
(atomic_read(&rdtp->dynticks) & 0x1))
@@ -635,7 +635,7 @@ void rcu_nmi_enter(void)
*/
void rcu_nmi_exit(void)
{
- struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
if (rdtp->dynticks_nmi_nesting == 0 ||
--rdtp->dynticks_nmi_nesting != 0)
@@ -658,7 +658,7 @@ int rcu_is_cpu_idle(void)
int ret;
preempt_disable();
- ret = (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0;
+ ret = (atomic_read(this_cpu_ptr(&rcu_dynticks).dynticks) & 0x1) == 0;
preempt_enable();
return ret;
}
@@ -696,7 +696,7 @@ bool rcu_lockdep_current_cpu_online(void)
if (in_nmi())
return 1;
preempt_disable();
- rdp = &__get_cpu_var(rcu_sched_data);
+ rdp = this_cpu_ptr(&rcu_sched_data);
rnp = rdp->mynode;
ret = (rdp->grpmask & rnp->qsmaskinit) ||
!rcu_scheduler_fully_active;
@@ -716,7 +716,7 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
*/
static int rcu_is_cpu_rrupt_from_idle(void)
{
- return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1;
+ return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
}
/*
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 7661875..e90b9c8 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -660,7 +660,7 @@ static void rcu_preempt_check_callbacks(int cpu)
static void rcu_preempt_do_callbacks(void)
{
- rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
+ rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
}
#endif /* #ifdef CONFIG_RCU_BOOST */
@@ -1332,7 +1332,7 @@ static void invoke_rcu_callbacks_kthread(void)
*/
static bool rcu_is_callbacks_kthread(void)
{
- return __get_cpu_var(rcu_cpu_kthread_task) == current;
+ return __this_cpu_read(rcu_cpu_kthread_task) == current;
}
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
@@ -1382,8 +1382,8 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
static void rcu_kthread_do_work(void)
{
- rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
- rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
+ rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
+ rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
rcu_preempt_do_callbacks();
}
@@ -1402,7 +1402,7 @@ static void rcu_cpu_kthread_park(unsigned int cpu)
static int rcu_cpu_kthread_should_run(unsigned int cpu)
{
- return __get_cpu_var(rcu_cpu_has_work);
+ return __this_cpu_read(rcu_cpu_has_work);
}
/*
@@ -1412,8 +1412,8 @@ static int rcu_cpu_kthread_should_run(unsigned int cpu)
*/
static void rcu_cpu_kthread(unsigned int cpu)
{
- unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status);
- char work, *workp = &__get_cpu_var(rcu_cpu_has_work);
+ unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
+ char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
int spincnt;
for (spincnt = 0; spincnt < 10; spincnt++) {
@@ -1638,7 +1638,7 @@ static bool rcu_try_advance_all_cbs(void)
{
bool cbs_ready = false;
struct rcu_data *rdp;
- struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
struct rcu_node *rnp;
struct rcu_state *rsp;
--
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