Mathieu Desnoyers wrote:
>
> This patch adds the ability to protect critical sections from migration to
> another CPU without disabling preemption.
>
> Typical use:
>
> migration_disable();
> local_inc(&__get_cpu_var(&my_local_t_var));
> migration_enable();
>
> --- linux-2.6-lttng.orig/kernel/sched.c 2007-07-05 16:28:15.000000000 -0400
> +++ linux-2.6-lttng/kernel/sched.c 2007-07-05 16:53:24.000000000 -0400
> @@ -1996,6 +1996,7 @@
> * 1) running (obviously), or
> * 2) cannot be migrated to this CPU due to cpus_allowed, or
> * 3) are cache-hot on their current CPU.
> + * 4) migration preemption is non 0 for this non running task.
> */
> if (!cpu_isset(this_cpu, p->cpus_allowed))
> return 0;
> @@ -2003,6 +2004,8 @@
>
> if (task_running(rq, p))
> return 0;
> + if (task_thread_info(p)->migration_count)
> + return 0;
Question: This means that the task could be preempted, but can't sleep, yes?
Because try_to_wake_up() can change ->cpu. Shouldn't might_sleep() check
->migration_count then? Or we can change try_to_wake_up().
What if the task does copy_process() under migration_disable() ? Child
gets a copy of ->migration_count.
Also, cpu_down() still can migrate this task to another CPU.
Oleg.
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