Messages in this thread Patch in this message | | | Subject | [patch] Re: rt scheduler may calculate wrong rt_time | From | Mike Galbraith <> | Date | Fri, 29 Apr 2011 08:36:50 +0200 |
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On Wed, 2011-04-27 at 19:51 +0200, Thomas Giesel wrote: > > Hm. Does forcing a clock update if we're idle when we release the > > throttle do the trick? > > It does. I tested it today and it works as expected. Even with ftrace I > couldn't see any suspicious behaviour anymore. > > Mike: Can you send the patch to the right people to get it into the > kernel or should I do it? Or is Peter the right one already?
Peter is the right one. Below is an ever so slightly different version.
sched, rt: update rq clock when unthrottling of an otherwise idle CPU
If an RT task is awakened while it's rt_rq is throttled, the time between wakeup/enqueue and unthrottle/selection may be accounted as rt_time if the CPU is idle. Set rq->skip_clock_update negative upon throttle release to tell put_prev_task() that we need a clock update.
Signed-off-by: Mike Galbraith <efault@gmx.de> Reported-by: Thomas Giesel <skoe@directbox.com>
--- kernel/sched.c | 6 +++--- kernel/sched_rt.c | 7 +++++++ 2 files changed, 10 insertions(+), 3 deletions(-)
Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c +++ linux-2.6/kernel/sched.c @@ -464,7 +464,7 @@ struct rq { u64 nohz_stamp; unsigned char nohz_balance_kick; #endif - unsigned int skip_clock_update; + int skip_clock_update; /* capture load from *all* tasks on this cpu: */ struct load_weight load; @@ -650,7 +650,7 @@ static void update_rq_clock(struct rq *r { s64 delta; - if (rq->skip_clock_update) + if (rq->skip_clock_update > 0) return; delta = sched_clock_cpu(cpu_of(rq)) - rq->clock; @@ -4125,7 +4125,7 @@ static inline void schedule_debug(struct static void put_prev_task(struct rq *rq, struct task_struct *prev) { - if (prev->on_rq) + if (prev->on_rq || rq->skip_clock_update < 0) update_rq_clock(rq); prev->sched_class->put_prev_task(rq, prev); } Index: linux-2.6/kernel/sched_rt.c =================================================================== --- linux-2.6.orig/kernel/sched_rt.c +++ linux-2.6/kernel/sched_rt.c @@ -562,6 +562,13 @@ static int do_sched_rt_period_timer(stru if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) { rt_rq->rt_throttled = 0; enqueue = 1; + + /* + * Force a clock update if the CPU was idle, + * lest wakeup -> unthrottle time accumulate. + */ + if (rt_rq->rt_nr_running && rq->curr == rq->idle) + rq->skip_clock_update = -1; } if (rt_rq->rt_time || rt_rq->rt_nr_running) idle = 0;
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