> > typedef struct {
> > unsigned int pad0;
> > unsigned int pad1;
> > unsigned int pad2;
> > unsigned int i;
> > unsigned int j;
> > unsigned int spin;
> You should mark at least 'spin' as volatile, otherwise bad optimization
> can occur...
> > static __inline__ unsigned int unique()
> > {
> > int ret;
> > __asm__ __volatile__( "rdtsc\n"
> > : "=eax" (ret)
> > : /* No inputs */
> > : "eax", "edx" );
> > return ret;
> And remove "eax" from list of used register to get it compile in gcc-2.95.2
> Parent:
> > while(pars->spin)
> > key = unique();
> > pars->spin += key;
> > if(pars->spin != key)
> > {
> > }
> > if(pars->i < pars->j)
> > fprintf(stderr, "i = %08x, j = %08x\n", pars->i, pars->j);
> > else
> > fprintf(stderr, "Good\n");
> > pars->spin -= key;
>
> Son:
> > while(pars->spin)
> > key = unique();
> > pars->spin += key;
> > pars->i++;
> > pars->j++;
> > pars->spin -= key;
> > }
> Look into code. Son is for any reason started first. While it does
>
> pars->spin -= key;
> while (pars->spin) key = unique();
> pars->spin += key;
>
> Operations: read, sub, write, read, compare, read, add, write
> So there is <------------------------->
> this window to switch to parent. But parent does
> while (pars->spin) key = unique();
> and this includes 'rdtsc' which is not very fast (and without -O2 it does
> also call/ret). If you add 'unique()' after 'pars->spin -= key;', it will
> happilly print couple of 'Good' (after some time it will core dump).
> Best regards,
> Petr Vandrovec
> vandrove@vc.cvut.cz
>
Compilation with -S -O2 show that no bad optimization is done.
In fact, the code works perfectly once the flush() macro was added.
If you core-dump and have the flush() macro, the problem is the missing
"$" in:
"\tpushl $1f\n"
|__ needs this.
Cheers,
Dick Johnson
Penguin : Linux version 2.3.13 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.
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