Message-Id: <00000140c67817eb-b582280a-f059-499f-a24c-a11f3d59b86e-000000@email.amazonses.com>
Date:	Wed, 28 Aug 2013 19:48:14 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [gcv v3 06/35] scheduler: 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 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>

Index: linux/include/linux/kernel_stat.h
===================================================================
--- linux.orig/include/linux/kernel_stat.h	2013-08-26 14:21:39.000000000 -0500
+++ linux/include/linux/kernel_stat.h	2013-08-26 14:23:08.883120293 -0500
@@ -47,8 +47,8 @@ DECLARE_PER_CPU(struct kernel_stat, ksta
 DECLARE_PER_CPU(struct kernel_cpustat, kernel_cpustat);
 
 /* Must have preemption disabled for this to be meaningful. */
-#define kstat_this_cpu (&__get_cpu_var(kstat))
-#define kcpustat_this_cpu (&__get_cpu_var(kernel_cpustat))
+#define kstat_this_cpu this_cpu_ptr(&kstat)
+#define kcpustat_this_cpu this_cpu_ptr(&kernel_cpustat)
 #define kstat_cpu(cpu) per_cpu(kstat, cpu)
 #define kcpustat_cpu(cpu) per_cpu(kernel_cpustat, cpu)
 
Index: linux/kernel/events/callchain.c
===================================================================
--- linux.orig/kernel/events/callchain.c	2013-08-26 14:21:39.000000000 -0500
+++ linux/kernel/events/callchain.c	2013-08-26 14:23:08.875120379 -0500
@@ -134,7 +134,7 @@ static struct perf_callchain_entry *get_
 	int cpu;
 	struct callchain_cpus_entries *entries;
 
-	*rctx = get_recursion_context(__get_cpu_var(callchain_recursion));
+	*rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
 	if (*rctx == -1)
 		return NULL;
 
@@ -150,7 +150,7 @@ static struct perf_callchain_entry *get_
 static void
 put_callchain_entry(int rctx)
 {
-	put_recursion_context(__get_cpu_var(callchain_recursion), rctx);
+	put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
 }
 
 struct perf_callchain_entry *
Index: linux/kernel/events/core.c
===================================================================
--- linux.orig/kernel/events/core.c	2013-08-26 14:21:39.000000000 -0500
+++ linux/kernel/events/core.c	2013-08-26 14:23:08.875120379 -0500
@@ -238,10 +238,10 @@ void perf_sample_event_took(u64 sample_l
 		return;
 
 	/* decay the counter by 1 average sample */
-	local_samples_len = __get_cpu_var(running_sample_length);
+	local_samples_len = __this_cpu_read(running_sample_length);
 	local_samples_len -= local_samples_len/NR_ACCUMULATED_SAMPLES;
 	local_samples_len += sample_len_ns;
-	__get_cpu_var(running_sample_length) = local_samples_len;
+	__this_cpu_write(running_sample_length, local_samples_len);
 
 	/*
 	 * note: this will be biased artifically low until we have
@@ -865,7 +865,7 @@ static DEFINE_PER_CPU(struct list_head,
 static void perf_pmu_rotate_start(struct pmu *pmu)
 {
 	struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
-	struct list_head *head = &__get_cpu_var(rotation_list);
+	struct list_head *head = this_cpu_ptr(&rotation_list);
 
 	WARN_ON(!irqs_disabled());
 
@@ -2321,7 +2321,7 @@ void __perf_event_task_sched_out(struct
 	 * to check if we have to switch out PMU state.
 	 * cgroup event are system-wide mode only
 	 */
-	if (atomic_read(&__get_cpu_var(perf_cgroup_events)))
+	if (atomic_read(this_cpu_ptr(&perf_cgroup_events)))
 		perf_cgroup_sched_out(task, next);
 }
 
@@ -2566,11 +2566,11 @@ void __perf_event_task_sched_in(struct t
 	 * to check if we have to switch in PMU state.
 	 * cgroup event are system-wide mode only
 	 */
-	if (atomic_read(&__get_cpu_var(perf_cgroup_events)))
+	if (atomic_read(this_cpu_ptr(&perf_cgroup_events)))
 		perf_cgroup_sched_in(prev, task);
 
 	/* check for system-wide branch_stack events */
-	if (atomic_read(&__get_cpu_var(perf_branch_stack_events)))
+	if (atomic_read(this_cpu_ptr(&perf_branch_stack_events)))
 		perf_branch_stack_sched_in(prev, task);
 }
 
@@ -2811,7 +2811,7 @@ done:
 #ifdef CONFIG_NO_HZ_FULL
 bool perf_event_can_stop_tick(void)
 {
-	if (list_empty(&__get_cpu_var(rotation_list)))
+	if (list_empty(this_cpu_ptr(&rotation_list)))
 		return true;
 	else
 		return false;
@@ -2820,7 +2820,7 @@ bool perf_event_can_stop_tick(void)
 
 void perf_event_task_tick(void)
 {
-	struct list_head *head = &__get_cpu_var(rotation_list);
+	struct list_head *head = this_cpu_ptr(&rotation_list);
 	struct perf_cpu_context *cpuctx, *tmp;
 	struct perf_event_context *ctx;
 	int throttled;
@@ -5414,7 +5414,7 @@ static void do_perf_sw_event(enum perf_t
 				    struct perf_sample_data *data,
 				    struct pt_regs *regs)
 {
-	struct swevent_htable *swhash = &__get_cpu_var(swevent_htable);
+	struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
 	struct perf_event *event;
 	struct hlist_head *head;
 
@@ -5433,7 +5433,7 @@ end:
 
 int perf_swevent_get_recursion_context(void)
 {
-	struct swevent_htable *swhash = &__get_cpu_var(swevent_htable);
+	struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
 
 	return get_recursion_context(swhash->recursion);
 }
@@ -5441,7 +5441,7 @@ EXPORT_SYMBOL_GPL(perf_swevent_get_recur
 
 inline void perf_swevent_put_recursion_context(int rctx)
 {
-	struct swevent_htable *swhash = &__get_cpu_var(swevent_htable);
+	struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
 
 	put_recursion_context(swhash->recursion, rctx);
 }
@@ -5470,7 +5470,7 @@ static void perf_swevent_read(struct per
 
 static int perf_swevent_add(struct perf_event *event, int flags)
 {
-	struct swevent_htable *swhash = &__get_cpu_var(swevent_htable);
+	struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
 	struct hw_perf_event *hwc = &event->hw;
 	struct hlist_head *head;
 
Index: linux/kernel/sched/cputime.c
===================================================================
--- linux.orig/kernel/sched/cputime.c	2013-08-26 14:21:39.000000000 -0500
+++ linux/kernel/sched/cputime.c	2013-08-26 14:23:08.879120335 -0500
@@ -121,7 +121,7 @@ static inline void task_group_account_fi
 	 * is the only cgroup, then nothing else should be necessary.
 	 *
 	 */
-	__get_cpu_var(kernel_cpustat).cpustat[index] += tmp;
+	__this_cpu_add(kernel_cpustat.cpustat[index], tmp);
 
 	cpuacct_account_field(p, index, tmp);
 }
Index: linux/kernel/sched/fair.c
===================================================================
--- linux.orig/kernel/sched/fair.c	2013-08-26 14:21:39.000000000 -0500
+++ linux/kernel/sched/fair.c	2013-08-26 14:23:08.879120335 -0500
@@ -5057,7 +5057,7 @@ static int load_balance(int this_cpu, st
 	struct sched_group *group;
 	struct rq *busiest;
 	unsigned long flags;
-	struct cpumask *cpus = __get_cpu_var(load_balance_mask);
+	struct cpumask *cpus = this_cpu_ptr(load_balance_mask);
 
 	struct lb_env env = {
 		.sd		= sd,
Index: linux/kernel/sched/rt.c
===================================================================
--- linux.orig/kernel/sched/rt.c	2013-08-26 14:21:39.000000000 -0500
+++ linux/kernel/sched/rt.c	2013-08-26 14:23:08.883120293 -0500
@@ -1389,7 +1389,7 @@ static DEFINE_PER_CPU(cpumask_var_t, loc
 static int find_lowest_rq(struct task_struct *task)
 {
 	struct sched_domain *sd;
-	struct cpumask *lowest_mask = __get_cpu_var(local_cpu_mask);
+	struct cpumask *lowest_mask = this_cpu_ptr(local_cpu_mask);
 	int this_cpu = smp_processor_id();
 	int cpu      = task_cpu(task);
 
Index: linux/kernel/sched/sched.h
===================================================================
--- linux.orig/kernel/sched/sched.h	2013-08-26 14:21:39.000000000 -0500
+++ linux/kernel/sched/sched.h	2013-08-26 14:23:08.883120293 -0500
@@ -538,10 +538,10 @@ static inline int cpu_of(struct rq *rq)
 DECLARE_PER_CPU(struct rq, runqueues);
 
 #define cpu_rq(cpu)		(&per_cpu(runqueues, (cpu)))
-#define this_rq()		(&__get_cpu_var(runqueues))
+#define this_rq()		this_cpu_ptr(&runqueues)
 #define task_rq(p)		cpu_rq(task_cpu(p))
 #define cpu_curr(cpu)		(cpu_rq(cpu)->curr)
-#define raw_rq()		(&__raw_get_cpu_var(runqueues))
+#define raw_rq()		__this_cpu_ptr(&runqueues)
 
 static inline u64 rq_clock(struct rq *rq)
 {
Index: linux/kernel/user-return-notifier.c
===================================================================
--- linux.orig/kernel/user-return-notifier.c	2013-08-26 14:21:39.000000000 -0500
+++ linux/kernel/user-return-notifier.c	2013-08-26 14:23:08.883120293 -0500
@@ -14,7 +14,7 @@ static DEFINE_PER_CPU(struct hlist_head,
 void user_return_notifier_register(struct user_return_notifier *urn)
 {
 	set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
-	hlist_add_head(&urn->link, &__get_cpu_var(return_notifier_list));
+	hlist_add_head(&urn->link, this_cpu_ptr(&return_notifier_list));
 }
 EXPORT_SYMBOL_GPL(user_return_notifier_register);
 
@@ -25,7 +25,7 @@ EXPORT_SYMBOL_GPL(user_return_notifier_r
 void user_return_notifier_unregister(struct user_return_notifier *urn)
 {
 	hlist_del(&urn->link);
-	if (hlist_empty(&__get_cpu_var(return_notifier_list)))
+	if (hlist_empty(this_cpu_ptr(&return_notifier_list)))
 		clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
 }
 EXPORT_SYMBOL_GPL(user_return_notifier_unregister);

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists