Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 16 Jun 2017 15:31:51 -0500 | Subject | Re: [RFC v2 1/2] swait: add idle variants which don't contribute to load average |
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"Luis R. Rodriguez" <mcgrof@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" <ebiederm@xmission.com> > Signed-off-by: Luis R. Rodriguez <mcgrof@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 */
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