On Tue, Aug 09, 2016 at 04:29:46PM -0400, Chris Metcalf wrote:
> +/*
> + * Each time we try to prepare for return to userspace in a process
> + * with task isolation enabled, we run this code to quiesce whatever
> + * subsystems we can readily quiesce to avoid later interrupts.
> + */
> +void task_isolation_enter(void)
> +{
> + WARN_ON_ONCE(irqs_disabled());
> +
> + /* Drain the pagevecs to avoid unnecessary IPI flushes later. */
> + lru_add_drain();
> +
> + /* Quieten the vmstat worker so it won't interrupt us. */
> + quiet_vmstat_sync();
So, this is going to be called everytime we resume to userspace
while in task isolation mode, right?
Do we need to quiesce vmstat everytime before entering userspace?
I thought that vmstat only need to be offlined once and for all?
And how about lru?
> +
> + /*
> + * Request rescheduling unless we are in full dynticks mode.
> + * We would eventually get pre-empted without this, and if
> + * there's another task waiting, it would run; but by
> + * explicitly requesting the reschedule, we may reduce the
> + * latency. We could directly call schedule() here as well,
> + * but since our caller is the standard place where schedule()
> + * is called, we defer to the caller.
> + *
> + * A more substantive approach here would be to use a struct
> + * completion here explicitly, and complete it when we shut
> + * down dynticks, but since we presumably have nothing better
> + * to do on this core anyway, just spinning seems plausible.
> + */
> + if (!tick_nohz_tick_stopped())
> + set_tsk_need_resched(current);
Again, that won't help :-)
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