"Luis R. Rodriguez" <mcg...@kernel.org> writes:
> There are cases where folks are using an interruptible swait when
> using kthreads. This is rather confusing given you'd expect
> interruptible waits to be -- interruptible, but kthreads are not
> interruptible ! The reason for such practice though is to avoid
> having these kthreads contribute to the system load average.
>
> When systems are idle some kthreads may spend a lot of time blocking if
> using swait_event_timeout(). This would contribute to the system load
> average. On systems without preemption this would mean the load average
> of an idle system is bumped to 2 instead of 0. On systems with PREEMPT=y
> this would mean the load average of an idle system is bumped to 3
> instead of 0.
>
> This adds proper API using TASK_IDLE to make such goals explicit and
> avoid confusion.
>
> Suggested-by: "Eric W. Biederman" <ebied...@xmission.com>
> Signed-off-by: Luis R. Rodriguez <mcg...@kernel.org>
> ---
> include/linux/swait.h | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/include/linux/swait.h b/include/linux/swait.h
> index 2c700694d50a..105c70e23286 100644
> --- a/include/linux/swait.h
> +++ b/include/linux/swait.h
> @@ -194,4 +194,29 @@ do {
> \
> __ret; \
> })
>
> +#define __swait_event_idle(wq, condition) \
> + ___swait_event(wq, condition, TASK_IDLE, 0, schedule())
> +
> +#define swait_event_idle(wq, condition)
> \
> +({ \
> + int __ret = 0; \
> + if (!(condition)) \
> + __ret = __swait_event_idle(wq, condition); \
> + __ret; \
> +})
The wait isn't interruptible so a return code doesn't make sense here.
> +#define __swait_event_idle_timeout(wq, condition, timeout) \
> + ___swait_event(wq, ___wait_cond_timeout(condition), \
> + TASK_IDLE, timeout, \
> + __ret = schedule_timeout(__ret))
> +
> +#define swait_event_idle_timeout(wq, condition, timeout) \
> +({ \
> + long __ret = timeout; \
> + if (!___wait_cond_timeout(condition)) \
> + __ret = __swait_event_idle_timeout(wq, \
> + condition, timeout); \
> + __ret; \
> +})
> +
> #endif /* _LINUX_SWAIT_H */
