Nigel Gamble wrote:
> A task that has been preempted is on the run queue and can be
> rescheduled on a different CPU, so I can't see how a per-CPU counter
> would work. It seems to me that you would need a per run queue
> counter, like the example I gave in a previous posting.
Ouch. What about all the per cpu structures in the kernel, how do you
handle them if a preempted task can be rescheduled on another cpu?
int count[NR_CPUS], *p;
p = count+smp_processor_id(); /* start on cpu 0, &count[0] */
if (*p >= 1024) {
/* preempt here, reschedule on cpu 1 */
*p = 1; /* update cpu 0 count from cpu 1, oops */
}
Unless you find every use of a per cpu structure and wrap a spin lock
around it, migrating a task from one cpu to another is going to be a
source of wierd and wonderful errors. Since the main use of per cpu
structures is to avoid locks, adding a spin lock to every structure
will be a killer. Or have I missed something?
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 21:00:15 EST