percpu: add optimized generic percpu accessors

It is an optimization and a cleanup, and adds the following new
generic percpu methods:

  percpu_read()
  percpu_write()
  percpu_add()
  percpu_sub()
  percpu_and()
  percpu_or()
  percpu_xor()

and implements support for them on x86. (other architectures will fall
back to a default implementation)

The advantage is that for example to read a local percpu variable,
instead of this sequence:

 return __get_cpu_var(var);

 ffffffff8102ca2b:	48 8b 14 fd 80 09 74 	mov    -0x7e8bf680(,%rdi,8),%rdx
 ffffffff8102ca32:	81
 ffffffff8102ca33:	48 c7 c0 d8 59 00 00 	mov    $0x59d8,%rax
 ffffffff8102ca3a:	48 8b 04 10          	mov    (%rax,%rdx,1),%rax

We can get a single instruction by using the optimized variants:

 return percpu_read(var);

 ffffffff8102ca3f:	65 48 8b 05 91 8f fd 	mov    %gs:0x7efd8f91(%rip),%rax

I also cleaned up the x86-specific APIs and made the x86 code use
these new generic percpu primitives.

tj: * fixed generic percpu_sub() definition as Roel Kluin pointed out
    * added percpu_and() for completeness's sake
    * made generic percpu ops atomic against preemption

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Tejun Heo <tj@kernel.org>

arch/x86/include/asm/current.h

@@ -10,7 +10,7 @@ struct task_struct;
 DECLARE_PER_CPU(struct task_struct *, current_task);
 static __always_inline struct task_struct *get_current(void)
 {
-	return x86_read_percpu(current_task);
+	return percpu_read(current_task);
 }
 
 #else /* X86_32 */

arch/x86/include/asm/irq_regs_32.h

@@ -15,7 +15,7 @@ DECLARE_PER_CPU(struct pt_regs *, irq_regs);
 
 static inline struct pt_regs *get_irq_regs(void)
 {
-	return x86_read_percpu(irq_regs);
+	return percpu_read(irq_regs);
 }
 
 static inline struct pt_regs *set_irq_regs(struct pt_regs *new_regs)
@@ -23,7 +23,7 @@ static inline struct pt_regs *set_irq_regs(struct pt_regs *new_regs)
 	struct pt_regs *old_regs;
 
 	old_regs = get_irq_regs();
-	x86_write_percpu(irq_regs, new_regs);
+	percpu_write(irq_regs, new_regs);
 
 	return old_regs;
 }

arch/x86/include/asm/mmu_context_32.h

@@ -4,8 +4,8 @@
 static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
 {
 #ifdef CONFIG_SMP
-	if (x86_read_percpu(cpu_tlbstate.state) == TLBSTATE_OK)
-		x86_write_percpu(cpu_tlbstate.state, TLBSTATE_LAZY);
+	if (percpu_read(cpu_tlbstate.state) == TLBSTATE_OK)
+		percpu_write(cpu_tlbstate.state, TLBSTATE_LAZY);
 #endif
 }
 
@@ -19,8 +19,8 @@ static inline void switch_mm(struct mm_struct *prev,
 		/* stop flush ipis for the previous mm */
 		cpu_clear(cpu, prev->cpu_vm_mask);
 #ifdef CONFIG_SMP
-		x86_write_percpu(cpu_tlbstate.state, TLBSTATE_OK);
-		x86_write_percpu(cpu_tlbstate.active_mm, next);
+		percpu_write(cpu_tlbstate.state, TLBSTATE_OK);
+		percpu_write(cpu_tlbstate.active_mm, next);
 #endif
 		cpu_set(cpu, next->cpu_vm_mask);
 
@@ -35,8 +35,8 @@ static inline void switch_mm(struct mm_struct *prev,
 	}
 #ifdef CONFIG_SMP
 	else {
-		x86_write_percpu(cpu_tlbstate.state, TLBSTATE_OK);
-		BUG_ON(x86_read_percpu(cpu_tlbstate.active_mm) != next);
+		percpu_write(cpu_tlbstate.state, TLBSTATE_OK);
+		BUG_ON(percpu_read(cpu_tlbstate.active_mm) != next);
 
 		if (!cpu_test_and_set(cpu, next->cpu_vm_mask)) {
 			/* We were in lazy tlb mode and leave_mm disabled

arch/x86/include/asm/pda.h

@@ -45,11 +45,11 @@ extern void pda_init(int);
 
 #define cpu_pda(cpu)		(&per_cpu(__pda, cpu))
 
-#define read_pda(field)		x86_read_percpu(__pda.field)
-#define write_pda(field, val)	x86_write_percpu(__pda.field, val)
-#define add_pda(field, val)	x86_add_percpu(__pda.field, val)
-#define sub_pda(field, val)	x86_sub_percpu(__pda.field, val)
-#define or_pda(field, val)	x86_or_percpu(__pda.field, val)
+#define read_pda(field)		percpu_read(__pda.field)
+#define write_pda(field, val)	percpu_write(__pda.field, val)
+#define add_pda(field, val)	percpu_add(__pda.field, val)
+#define sub_pda(field, val)	percpu_sub(__pda.field, val)
+#define or_pda(field, val)	percpu_or(__pda.field, val)
 
 /* This is not atomic against other CPUs -- CPU preemption needs to be off */
 #define test_and_clear_bit_pda(bit, field)				\

arch/x86/include/asm/percpu.h

@@ -40,16 +40,11 @@
 
 #ifdef CONFIG_SMP
 #define __percpu_seg_str	"%%"__stringify(__percpu_seg)":"
-#define __my_cpu_offset		x86_read_percpu(this_cpu_off)
+#define __my_cpu_offset		percpu_read(this_cpu_off)
 #else
 #define __percpu_seg_str
 #endif
 
-#include <asm-generic/percpu.h>
-
-/* We can use this directly for local CPU (faster). */
-DECLARE_PER_CPU(unsigned long, this_cpu_off);
-
 /* For arch-specific code, we can use direct single-insn ops (they
  * don't give an lvalue though). */
 extern void __bad_percpu_size(void);
@@ -115,11 +110,13 @@ do {							\
 	ret__;						\
 })
 
-#define x86_read_percpu(var) percpu_from_op("mov", per_cpu__##var)
-#define x86_write_percpu(var, val) percpu_to_op("mov", per_cpu__##var, val)
-#define x86_add_percpu(var, val) percpu_to_op("add", per_cpu__##var, val)
-#define x86_sub_percpu(var, val) percpu_to_op("sub", per_cpu__##var, val)
-#define x86_or_percpu(var, val) percpu_to_op("or", per_cpu__##var, val)
+#define percpu_read(var)	percpu_from_op("mov", per_cpu__##var)
+#define percpu_write(var, val)	percpu_to_op("mov", per_cpu__##var, val)
+#define percpu_add(var, val)	percpu_to_op("add", per_cpu__##var, val)
+#define percpu_sub(var, val)	percpu_to_op("sub", per_cpu__##var, val)
+#define percpu_and(var, val)	percpu_to_op("and", per_cpu__##var, val)
+#define percpu_or(var, val)	percpu_to_op("or", per_cpu__##var, val)
+#define percpu_xor(var, val)	percpu_to_op("xor", per_cpu__##var, val)
 
 /* This is not atomic against other CPUs -- CPU preemption needs to be off */
 #define x86_test_and_clear_bit_percpu(bit, var)				\
@@ -131,6 +128,11 @@ do {							\
 	old__;								\
 })
 
+#include <asm-generic/percpu.h>
+
+/* We can use this directly for local CPU (faster). */
+DECLARE_PER_CPU(unsigned long, this_cpu_off);
+
 #ifdef CONFIG_X86_64
 extern void load_pda_offset(int cpu);
 #else

arch/x86/include/asm/smp.h

@@ -160,7 +160,7 @@ extern unsigned disabled_cpus __cpuinitdata;
  * from the initial startup. We map APIC_BASE very early in page_setup(),
  * so this is correct in the x86 case.
  */
-#define raw_smp_processor_id() (x86_read_percpu(cpu_number))
+#define raw_smp_processor_id() (percpu_read(cpu_number))
 extern int safe_smp_processor_id(void);
 
 #elif defined(CONFIG_X86_64_SMP)

arch/x86/kernel/process_32.c

@@ -591,7 +591,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	if (prev->gs | next->gs)
 		loadsegment(gs, next->gs);
 
-	x86_write_percpu(current_task, next_p);
+	percpu_write(current_task, next_p);
 
 	return prev_p;
 }

arch/x86/kernel/tlb_32.c

@@ -34,8 +34,8 @@ static DEFINE_SPINLOCK(tlbstate_lock);
  */
 void leave_mm(int cpu)
 {
-	BUG_ON(x86_read_percpu(cpu_tlbstate.state) == TLBSTATE_OK);
-	cpu_clear(cpu, x86_read_percpu(cpu_tlbstate.active_mm)->cpu_vm_mask);
+	BUG_ON(percpu_read(cpu_tlbstate.state) == TLBSTATE_OK);
+	cpu_clear(cpu, percpu_read(cpu_tlbstate.active_mm)->cpu_vm_mask);
 	load_cr3(swapper_pg_dir);
 }
 EXPORT_SYMBOL_GPL(leave_mm);
@@ -103,8 +103,8 @@ void smp_invalidate_interrupt(struct pt_regs *regs)
 		 * BUG();
 		 */
 
-	if (flush_mm == x86_read_percpu(cpu_tlbstate.active_mm)) {
-		if (x86_read_percpu(cpu_tlbstate.state) == TLBSTATE_OK) {
+	if (flush_mm == percpu_read(cpu_tlbstate.active_mm)) {
+		if (percpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
 			if (flush_va == TLB_FLUSH_ALL)
 				local_flush_tlb();
 			else
@@ -222,7 +222,7 @@ static void do_flush_tlb_all(void *info)
 	unsigned long cpu = smp_processor_id();
 
 	__flush_tlb_all();
-	if (x86_read_percpu(cpu_tlbstate.state) == TLBSTATE_LAZY)
+	if (percpu_read(cpu_tlbstate.state) == TLBSTATE_LAZY)
 		leave_mm(cpu);
 }
 

arch/x86/mach-voyager/voyager_smp.c

@@ -402,7 +402,7 @@ void __init find_smp_config(void)
 	     VOYAGER_SUS_IN_CONTROL_PORT);
 
 	current_thread_info()->cpu = boot_cpu_id;
-	x86_write_percpu(cpu_number, boot_cpu_id);
+	percpu_write(cpu_number, boot_cpu_id);
 }
 
 /*
@@ -1782,7 +1782,7 @@ static void __init voyager_smp_cpus_done(unsigned int max_cpus)
 void __init smp_setup_processor_id(void)
 {
 	current_thread_info()->cpu = hard_smp_processor_id();
-	x86_write_percpu(cpu_number, hard_smp_processor_id());
+	percpu_write(cpu_number, hard_smp_processor_id());
 }
 
 static void voyager_send_call_func(cpumask_t callmask)

arch/x86/xen/enlighten.c

@@ -695,17 +695,17 @@ static void xen_write_cr0(unsigned long cr0)
 
 static void xen_write_cr2(unsigned long cr2)
 {
-	x86_read_percpu(xen_vcpu)->arch.cr2 = cr2;
+	percpu_read(xen_vcpu)->arch.cr2 = cr2;
 }
 
 static unsigned long xen_read_cr2(void)
 {
-	return x86_read_percpu(xen_vcpu)->arch.cr2;
+	return percpu_read(xen_vcpu)->arch.cr2;
 }
 
 static unsigned long xen_read_cr2_direct(void)
 {
-	return x86_read_percpu(xen_vcpu_info.arch.cr2);
+	return percpu_read(xen_vcpu_info.arch.cr2);
 }
 
 static void xen_write_cr4(unsigned long cr4)
@@ -718,12 +718,12 @@ static void xen_write_cr4(unsigned long cr4)
 
 static unsigned long xen_read_cr3(void)
 {
-	return x86_read_percpu(xen_cr3);
+	return percpu_read(xen_cr3);
 }
 
 static void set_current_cr3(void *v)
 {
-	x86_write_percpu(xen_current_cr3, (unsigned long)v);
+	percpu_write(xen_current_cr3, (unsigned long)v);
 }
 
 static void __xen_write_cr3(bool kernel, unsigned long cr3)
@@ -748,7 +748,7 @@ static void __xen_write_cr3(bool kernel, unsigned long cr3)
 	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 
 	if (kernel) {
-		x86_write_percpu(xen_cr3, cr3);
+		percpu_write(xen_cr3, cr3);
 
 		/* Update xen_current_cr3 once the batch has actually
 		   been submitted. */
@@ -764,7 +764,7 @@ static void xen_write_cr3(unsigned long cr3)
 
 	/* Update while interrupts are disabled, so its atomic with
 	   respect to ipis */
-	x86_write_percpu(xen_cr3, cr3);
+	percpu_write(xen_cr3, cr3);
 
 	__xen_write_cr3(true, cr3);
 

arch/x86/xen/irq.c

@@ -39,7 +39,7 @@ static unsigned long xen_save_fl(void)
 	struct vcpu_info *vcpu;
 	unsigned long flags;
 
-	vcpu = x86_read_percpu(xen_vcpu);
+	vcpu = percpu_read(xen_vcpu);
 
 	/* flag has opposite sense of mask */
 	flags = !vcpu->evtchn_upcall_mask;
@@ -62,7 +62,7 @@ static void xen_restore_fl(unsigned long flags)
 	   make sure we're don't switch CPUs between getting the vcpu
 	   pointer and updating the mask. */
 	preempt_disable();
-	vcpu = x86_read_percpu(xen_vcpu);
+	vcpu = percpu_read(xen_vcpu);
 	vcpu->evtchn_upcall_mask = flags;
 	preempt_enable_no_resched();
 
@@ -83,7 +83,7 @@ static void xen_irq_disable(void)
 	   make sure we're don't switch CPUs between getting the vcpu
 	   pointer and updating the mask. */
 	preempt_disable();
-	x86_read_percpu(xen_vcpu)->evtchn_upcall_mask = 1;
+	percpu_read(xen_vcpu)->evtchn_upcall_mask = 1;
 	preempt_enable_no_resched();
 }
 
@@ -96,7 +96,7 @@ static void xen_irq_enable(void)
 	   the caller is confused and is trying to re-enable interrupts
 	   on an indeterminate processor. */
 
-	vcpu = x86_read_percpu(xen_vcpu);
+	vcpu = percpu_read(xen_vcpu);
 	vcpu->evtchn_upcall_mask = 0;
 
 	/* Doesn't matter if we get preempted here, because any

arch/x86/xen/mmu.c

@@ -1074,7 +1074,7 @@ static void drop_other_mm_ref(void *info)
 
 	/* If this cpu still has a stale cr3 reference, then make sure
 	   it has been flushed. */
-	if (x86_read_percpu(xen_current_cr3) == __pa(mm->pgd)) {
+	if (percpu_read(xen_current_cr3) == __pa(mm->pgd)) {
 		load_cr3(swapper_pg_dir);
 		arch_flush_lazy_cpu_mode();
 	}

arch/x86/xen/multicalls.h

@@ -39,7 +39,7 @@ static inline void xen_mc_issue(unsigned mode)
 		xen_mc_flush();
 
 	/* restore flags saved in xen_mc_batch */
-	local_irq_restore(x86_read_percpu(xen_mc_irq_flags));
+	local_irq_restore(percpu_read(xen_mc_irq_flags));
 }
 
 /* Set up a callback to be called when the current batch is flushed */

arch/x86/xen/smp.c

@@ -78,7 +78,7 @@ static __cpuinit void cpu_bringup(void)
 	xen_setup_cpu_clockevents();
 
 	cpu_set(cpu, cpu_online_map);
-	x86_write_percpu(cpu_state, CPU_ONLINE);
+	percpu_write(cpu_state, CPU_ONLINE);
 	wmb();
 
 	/* We can take interrupts now: we're officially "up". */

include/asm-generic/percpu.h

@@ -80,4 +80,56 @@ extern void setup_per_cpu_areas(void);
 #define DECLARE_PER_CPU(type, name) extern PER_CPU_ATTRIBUTES \
 					__typeof__(type) per_cpu_var(name)
 
+/*
+ * Optional methods for optimized non-lvalue per-cpu variable access.
+ *
+ * @var can be a percpu variable or a field of it and its size should
+ * equal char, int or long.  percpu_read() evaluates to a lvalue and
+ * all others to void.
+ *
+ * These operations are guaranteed to be atomic w.r.t. preemption.
+ * The generic versions use plain get/put_cpu_var().  Archs are
+ * encouraged to implement single-instruction alternatives which don't
+ * require preemption protection.
+ */
+#ifndef percpu_read
+# define percpu_read(var)						\
+  ({									\
+	typeof(per_cpu_var(var)) __tmp_var__;				\
+	__tmp_var__ = get_cpu_var(var);					\
+	put_cpu_var(var);						\
+	__tmp_var__;							\
+  })
+#endif
+
+#define __percpu_generic_to_op(var, val, op)				\
+do {									\
+	get_cpu_var(var) op val;					\
+	put_cpu_var(var);						\
+} while (0)
+
+#ifndef percpu_write
+# define percpu_write(var, val)		__percpu_generic_to_op(var, (val), =)
+#endif
+
+#ifndef percpu_add
+# define percpu_add(var, val)		__percpu_generic_to_op(var, (val), +=)
+#endif
+
+#ifndef percpu_sub
+# define percpu_sub(var, val)		__percpu_generic_to_op(var, (val), -=)
+#endif
+
+#ifndef percpu_and
+# define percpu_and(var, val)		__percpu_generic_to_op(var, (val), &=)
+#endif
+
+#ifndef percpu_or
+# define percpu_or(var, val)		__percpu_generic_to_op(var, (val), |=)
+#endif
+
+#ifndef percpu_xor
+# define percpu_xor(var, val)		__percpu_generic_to_op(var, (val), ^=)
+#endif
+
 #endif /* _ASM_GENERIC_PERCPU_H_ */