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>

1 files changed, 7 insertions, 7 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 312414ef9365..75b94139e1f2 100644
--- a/arch/x86/xen/enlighten.c
+++ b/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);