On Fri, 2013-02-22 at 13:50 +0100, Frederic Weisbecker wrote: > > Which is a problem how? > > So here is a possible scenario, CPU 0 reads a kcpustat value, and CPU > 1 writes > it at the same time: > > //Initial value of "cpustat" is 0xffffffff > == CPU 0 == == CPU 1 == > > //load low part > mov %eax, [cpustat] > inc [cpustat] > //Update the high part if necessary > jnc 1f > inc [cpustat + 4] > 1: > //load high part > mov %edx, [cpustat + 4] > > > Afterward, CPU 0 will think the value is 0x1ffffffff while it's > actually > 0x100000000. > > atomic64_read() and atomic64_set() are supposed to take care of that, > without > even the need for _inc() or _add() parts that use LOCK.
Sure I get that, but again, why is that a problem,.. who relies on these statistics that makes it a problem? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
