[question] Can the execution of the atomtic operation instruction pair lwarx/stwcx be interrrupted by local HW interruptions?

[Gavin Hu]

Thanks your response.  :)
But that means that these optimitive operations like atomic_add() aren't
optimitive actully in PPC architecture, right? Becuase they can be
interrupted by loacl HW interrupts. Theoretically, the ISR also can access
the atomic gloable variable.


The following codes are complete atomic_inc() copied from arch/
static __inline__ void atomic_add(int a, atomic_t *v)
{
    int t;

    __asm__ __volatile__(
"1:    lwarx    %0,0,%3        # atomic_add\n\
    add    %0,%2,%0\n"
    PPC405_ERR77(0,%3)
"    stwcx.    %0,0,%3 \n\
    bne-    1b"
    : "=&r" (t), "+m" (v->counter)
    : "r" (a), "r" (&v->counter)
    : "cc");
}


BR
Gavin. Hu


On Mon, Dec 30, 2013 at 9:54 AM, wyang <w90p710 at gmail.com> wrote:

>  On 12/28/2013 01:41 PM, Gavin Hu wrote:
>
> Hi
>
> I notice that there is a pair ppc instructions lwarx and stwcx used to
> atomtic operation for instance, atomic_inc/atomic_dec.
>
>  In some ppc manuals, they more emphasize its mechanism is that lwarx can
> reseve the target memory address preventing other CORE from modifying it.
>
>  I assume that there is atomtic operation executing on the CORE0 in a
> multicore system. In this situation, does the CORE0 disable the local HW
> interrupt?
>  Can the executing process from the beginning of lwarx and end of stwcx
> be interrupted by HW interruptions/exceptions?  Anyway, they are two
> assembly instructions.
>
>
> It should just like other arch, the processor should response any
> interrupt after the execution of a instruction, so the local HW interrupt
> is not disabled.
>
> Thanks
> Wei
>
>
>  Thanks a lot!
>
> "1:    lwarx    %0,0,%2        # atomic_inc\n\
>     addic    %0,%0,1\n"
> "    stwcx.    %0,0,%2 \n\
>
>
>  BR
>  Gavin. Hu
>
>
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>
>
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