On Tue, 2010-06-22 at 21:52 +0800, Wu Fengguang wrote:

#include <stdio.h> 

typedef struct {
        int counter;
} atomic_t;

static inline int atomic_dec_and_test(atomic_t *v)
{      
        unsigned char c;

        asm volatile("lock; decl %0; sete %1"
                     : "+m" (v->counter), "=qm" (c)
                     : : "memory");
        return c != 0;
}

int main(void)
{ 
        atomic_t i;

        i.counter = 100000000;

        for (; !atomic_dec_and_test(&i);)
                ;

        return 0;
} 

This test utterly fails to stress the concurrency, you want to create
nr_cpus threads and then pound the global variable. Then compare it
against the per-cpu-counter variant.


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