• Ingo Molnar's avatar
    percpu: add optimized generic percpu accessors · 6dbde353
    Ingo Molnar authored
    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: default avatarIngo Molnar <mingo@elte.hu>
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    6dbde353
irq_regs_32.h 642 Bytes