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sched: Expire invalid runtime

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Since quota is managed using a global state but consumed on a per-cpu basis
we need to ensure that our per-cpu state is appropriately synchronized.
Most importantly, runtime that is state (from a previous period) should not be
locally consumable.

We take advantage of existing sched_clock synchronization about the jiffy to
efficiently detect whether we have (globally) crossed a quota boundary above.

One catch is that the direction of spread on sched_clock is undefined,
specifically, we don't know whether our local clock is behind or ahead
of the one responsible for the current expiration time.

Fortunately we can differentiate these by considering whether the
global deadline has advanced.  If it has not, then we assume our clock to be
"fast" and advance our local expiration; otherwise, we know the deadline has
truly passed and we expire our local runtime.

Signed-off-by: Paul Turner <pjt@google.com>
Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110721184757.379275352@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul Turner 2011-07-21 09:43:32 -07:00 • committed by Ingo Molnar
parent 58088ad015
commit a9cf55b286
2 changed files with 84 additions and 10 deletions
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4
kernel/sched.c
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@ -256,6 +256,7 @@ struct cfs_bandwidth {
ktime_t period;
u64 quota, runtime;
s64 hierarchal_quota;
u64 runtime_expires;
int idle, timer_active;
struct hrtimer period_timer;
@ -396,6 +397,7 @@ struct cfs_rq {
#endif
#ifdef CONFIG_CFS_BANDWIDTH
int runtime_enabled;
u64 runtime_expires;
s64 runtime_remaining;
#endif
#endif
@ -9166,8 +9168,8 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
raw_spin_lock_irq(&cfs_b->lock);
cfs_b->period = ns_to_ktime(period);
cfs_b->quota = quota;
cfs_b->runtime = quota;
__refill_cfs_bandwidth_runtime(cfs_b);
/* restart the period timer (if active) to handle new period expiry */
if (runtime_enabled && cfs_b->timer_active) {
/* force a reprogram */