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Date: Thu, 24 Mar 2011 12:06:43 +0530
From: Bharata B Rao <bharata@...ux.vnet.ibm.com>
To: Paul Turner <pjt@...gle.com>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Dhaval Giani <dhaval.giani@...il.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Pavel Emelyanov <xemul@...nvz.org>,
Nikhil Rao <ncrao@...gle.com>
Subject: Re: [patch 04/15] sched: throttle cfs_rq entities which exceed their
local quota
On Tue, Mar 22, 2011 at 08:03:30PM -0700, Paul Turner wrote:
> In account_cfs_rq_quota() (via update_curr()) we track consumption versus a
> cfs_rqs locally assigned quota and whether there is global quota available
> to provide a refill when it runs out.
>
> In the case that there is no quota remaining it's necessary to throttle so
> that execution ceases until the susbequent period. While it is at this
> boundary that we detect (and signal for, via reshed_task) that a throttle is
> required, the actual operation is deferred until put_prev_entity().
>
> At this point the cfs_rq is marked as throttled and not re-enqueued, this
> avoids potential interactions with throttled runqueues in the event that we
> are not immediately able to evict the running task.
>
> Signed-off-by: Paul Turner <pjt@...gle.com>
> Signed-off-by: Nikhil Rao <ncrao@...gle.com>
> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> ---
> kernel/sched.c | 2
> kernel/sched_fair.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++---
> 2 files changed, 113 insertions(+), 6 deletions(-)
>
> Index: tip/kernel/sched.c
> ===================================================================
> --- tip.orig/kernel/sched.c
> +++ tip/kernel/sched.c
> @@ -386,7 +386,7 @@ struct cfs_rq {
> unsigned long load_contribution;
> #endif
> #ifdef CONFIG_CFS_BANDWIDTH
> - int quota_enabled;
> + int quota_enabled, throttled;
> s64 quota_remaining;
> #endif
> #endif
> Index: tip/kernel/sched_fair.c
> ===================================================================
> --- tip.orig/kernel/sched_fair.c
> +++ tip/kernel/sched_fair.c
> @@ -321,9 +321,6 @@ find_matching_se(struct sched_entity **s
>
> #endif /* CONFIG_FAIR_GROUP_SCHED */
>
> -static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
> - unsigned long delta_exec);
> -
> /**************************************************************
> * Scheduling class tree data structure manipulation methods:
> */
> @@ -588,6 +585,9 @@ __update_curr(struct cfs_rq *cfs_rq, str
> #endif
> }
>
> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
> + unsigned long delta_exec);
> +
> static void update_curr(struct cfs_rq *cfs_rq)
> {
> struct sched_entity *curr = cfs_rq->curr;
> @@ -1221,6 +1221,9 @@ static struct sched_entity *pick_next_en
> return se;
> }
>
> +static void throttle_cfs_rq(struct cfs_rq *cfs_rq);
> +static inline int within_bandwidth(struct cfs_rq *cfs_rq);
> +
> static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
> {
> /*
> @@ -1230,6 +1233,9 @@ static void put_prev_entity(struct cfs_r
> if (prev->on_rq)
> update_curr(cfs_rq);
>
> + if (!within_bandwidth(cfs_rq))
> + throttle_cfs_rq(cfs_rq);
> +
> check_spread(cfs_rq, prev);
> if (prev->on_rq) {
> update_stats_wait_start(cfs_rq, prev);
> @@ -1241,6 +1247,8 @@ static void put_prev_entity(struct cfs_r
> cfs_rq->curr = NULL;
> }
>
> +static void check_cfs_rq_quota(struct cfs_rq *cfs_rq);
> +
> static void
> entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
> {
> @@ -1249,6 +1257,9 @@ entity_tick(struct cfs_rq *cfs_rq, struc
> */
> update_curr(cfs_rq);
>
> + /* check that entity's usage is still within quota (if enabled) */
> + check_cfs_rq_quota(cfs_rq);
> +
> /*
> * Update share accounting for long-running entities.
> */
> @@ -1294,6 +1305,46 @@ static inline u64 sched_cfs_bandwidth_sl
> return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
> }
>
> +static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
> +{
> + return cfs_rq->throttled;
> +}
> +
> +static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
> +{
> + struct task_group *tg;
> + struct sched_entity *se;
> +
> + if (cfs_rq_throttled(cfs_rq))
> + return 1;
> +
> + tg = cfs_rq->tg;
> + se = tg->se[cpu_of(rq_of(cfs_rq))];
> + if (!se)
> + return 0;
> +
> + for_each_sched_entity(se) {
> + if (cfs_rq_throttled(cfs_rq_of(se)))
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +static inline int within_bandwidth(struct cfs_rq *cfs_rq)
> +{
> + return !cfs_rq->quota_enabled || cfs_rq->quota_remaining > 0;
> +}
> +
> +static void check_cfs_rq_quota(struct cfs_rq *cfs_rq)
> +{
> + if (within_bandwidth(cfs_rq))
> + return;
> +
> +
> + resched_task(rq_of(cfs_rq)->curr);
> +}
> +
> static void request_cfs_rq_quota(struct cfs_rq *cfs_rq)
> {
> struct task_group *tg = cfs_rq->tg;
> @@ -1330,6 +1381,29 @@ static void account_cfs_rq_quota(struct
> request_cfs_rq_quota(cfs_rq);
> }
>
> +static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
> +{
> + struct sched_entity *se;
> +
> + se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
> +
> + /* account load preceding throttle */
> + update_cfs_load(cfs_rq, 0);
> +
> + for_each_sched_entity(se) {
> + struct cfs_rq *qcfs_rq = cfs_rq_of(se);
> + /* throttled entity or throttle-on-deactivate */
> + if (!se->on_rq)
> + break;
> +
> + dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
> + if (qcfs_rq->load.weight)
> + break;
> + }
> +
> + cfs_rq->throttled = 1;
> +}
Since throttling is done from put_prev_entity(), iiuc, you will be
doing 'put' for current entities which are not on the tree. Can you
avoid the dequeue_entity() call here which I think will anyway bail out
from actual dequeueing (se != cfs_rq->curr check in dequeue_entity).
Regards,
Bharata.
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