From: Mike Galbraith <efault@gmx.de>
To: Thomas Giesel <skoe@directbox.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: [patch] Re: rt scheduler may calculate wrong rt_time
Date: Fri, 29 Apr 2011 08:36:50 +0200 [thread overview]
Message-ID: <1304059010.7472.1.camel@marge.simson.net> (raw)
In-Reply-To: <20110427195113.4e0064bb@acer>
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;
next prev parent reply other threads:[~2011-04-29 6:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-21 12:55 rt scheduler may calculate wrong rt_time Thomas Giesel
2011-04-22 8:21 ` Mike Galbraith
2011-04-22 20:52 ` Thomas Giesel
2011-04-27 17:51 ` Thomas Giesel
2011-04-29 6:36 ` Mike Galbraith [this message]
2011-05-16 10:37 ` [tip:sched/core] sched, rt: Update rq clock when unthrottling of an otherwise idle CPU tip-bot for Mike Galbraith
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