Le vendredi 19 novembre 2010 Ã 09:59 -0600, Christoph Lameter a Ãcrit :
> On Fri, 19 Nov 2010, Eric Dumazet wrote:
>
> > > This isnt a use case for this_cpu_dec right? Seems that your message was
> > > cut off?
> > I wanted to show you the file were it was possible to use this_cpu_{dec|
> > inc}_return()
> >
> > My patch on kmap_atomic_idx() doesnt need your new functions ;)
>
> Oh ok you mean this:
>
> ---
> include/linux/highmem.h | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> Index: linux-2.6/include/linux/highmem.h
> ===================================================================
> --- linux-2.6.orig/include/linux/highmem.h 2010-11-19 09:55:24.000000000 -0600
> +++ linux-2.6/include/linux/highmem.h 2010-11-19 09:57:54.000000000 -0600
> @@ -81,7 +81,9 @@ DECLARE_PER_CPU(int, __kmap_atomic_idx);
>
> static inline int kmap_atomic_idx_push(void)
> {
> - int idx = __get_cpu_var(__kmap_atomic_idx)++;
> + int idx = __this_cpu_read(__kmap_atomic_idx);
> +
> + __this_cpu_inc(__kmap_atomic_idx);
> #ifdef CONFIG_DEBUG_HIGHMEM
> WARN_ON_ONCE(in_irq() && !irqs_disabled());
> BUG_ON(idx > KM_TYPE_NR);
> @@ -91,12 +93,12 @@ static inline int kmap_atomic_idx_push(v
>
> static inline int kmap_atomic_idx(void)
> {
> - return __get_cpu_var(__kmap_atomic_idx) - 1;
> + return __this_cpu_read(__kmap_atomic_idx) - 1;
> }
>
> static inline int kmap_atomic_idx_pop(void)
> {
> - int idx = --__get_cpu_var(__kmap_atomic_idx);
> + int idx = __this_cpu_dec_return(__kmap_atomic_idx);
> #ifdef CONFIG_DEBUG_HIGHMEM
> BUG_ON(idx < 0);
> #endif
Yes, absolutely.
By the way, is your patch really ok ?
xadd %0,foo returns in %0 the previous value of the memory, not the
value _after_ the operation.
This is why we do in arch/x86/include/asm/atomic.h :
static inline int atomic_add_return(int i, atomic_t *v)
...
__i = i;
asm volatile(LOCK_PREFIX "xaddl %0, %1"
: "+r" (i), "+m" (v->counter)
: : "memory");
return i + __i;
...
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