Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932654Ab2F1GKG (ORCPT ); Thu, 28 Jun 2012 02:10:06 -0400 Received: from LGEMRELSE1Q.lge.com ([156.147.1.111]:47854 "EHLO LGEMRELSE1Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932579Ab2F1GKB (ORCPT ); Thu, 28 Jun 2012 02:10:01 -0400 X-AuditID: 9c93016f-b7c85ae00000559e-3a-4febf537d055 From: Namhyung Kim To: Paul Turner Cc: linux-kernel@vger.kernel.org, Venki Pallipadi , Srivatsa Vaddagiri , Vincent Guittot , Peter Zijlstra , Nikunj A Dadhania , Mike Galbraith , Kamalesh Babulal , Ben Segall , Ingo Molnar , "Paul E. McKenney" , Morten Rasmussen , Vaidyanathan Srinivasan Subject: Re: [PATCH 01/16] sched: track the runnable average on a per-task entitiy basis References: <20120628022413.30496.32798.stgit@kitami.mtv.corp.google.com> <20120628022414.30496.98256.stgit@kitami.mtv.corp.google.com> Date: Thu, 28 Jun 2012 15:06:10 +0900 In-Reply-To: <20120628022414.30496.98256.stgit@kitami.mtv.corp.google.com> (Paul Turner's message of "Wed, 27 Jun 2012 19:24:14 -0700") Message-ID: <87pq8kx965.fsf@sejong.aot.lge.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.97 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8041 Lines: 261 Hi, Some nitpicks and questions. On Wed, 27 Jun 2012 19:24:14 -0700, Paul Turner wrote: > Instead of tracking averaging the load parented by a cfs_rq, we can track > entity load directly. With the load for a given cfs_Rq then being the sum of s/cfs_Rq/cfs_rq/ > its children. > > To do this we represent the historical contribution to runnable average within each > trailing 1024us of execution as the coefficients of a geometric series. > > We can express this for a given task t as: > runnable_sum(t) = \Sum u_i * y^i , > load(t) = weight_t * runnable_sum(t) / (\Sum 1024 * y^i) > This "\Sum 1024 *y^i" is the runnable(_avg)_period, right? > Where: u_i is the usage in the last i`th 1024us period (approximately 1ms) ~ms > and y is chosen such that y^k = 1/2. We currently choose k to be 32 which > roughly translates to about a sched period. > > Signed-off-by: Paul Turner > --- > include/linux/sched.h | 8 +++ > kernel/sched/debug.c | 4 ++ > kernel/sched/fair.c | 128 +++++++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 140 insertions(+), 0 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 9dced2e..5bf5c79 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1136,6 +1136,11 @@ struct load_weight { > unsigned long weight, inv_weight; > }; > > +struct sched_avg { > + u32 runnable_avg_sum, runnable_avg_period; > + u64 last_runnable_update; > +}; > + > #ifdef CONFIG_SCHEDSTATS > struct sched_statistics { > u64 wait_start; > @@ -1196,6 +1201,9 @@ struct sched_entity { > /* rq "owned" by this entity/group: */ > struct cfs_rq *my_q; > #endif > +#ifdef CONFIG_SMP > + struct sched_avg avg; > +#endif > }; > > struct sched_rt_entity { > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c > index c09a4e7..cd5ef23 100644 > --- a/kernel/sched/debug.c > +++ b/kernel/sched/debug.c > @@ -85,6 +85,10 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group > P(se->statistics.wait_count); > #endif > P(se->load.weight); > +#ifdef CONFIG_SMP > + P(se->avg.runnable_avg_sum); > + P(se->avg.runnable_avg_period); > +#endif > #undef PN > #undef P > } > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 3704ad3..864a122 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -976,6 +976,125 @@ static inline void update_entity_shares_tick(struct cfs_rq *cfs_rq) > } > #endif /* CONFIG_FAIR_GROUP_SCHED */ > > +#ifdef CONFIG_SMP > +/* > + * Approximate: > + * val * y^n, where y^32 ~= 0.5 (~1 scheduling period) > + */ > +static __always_inline u64 decay_load(u64 val, int n) > +{ > + for (; n && val; n--) { > + val *= 4008; > + val >>= 12; > + } > + > + return val; > +} > + > +/* We can represent the historical contribution to runnable average as the > + * coefficients of a geometric series. To do this we sub-divide our runnable > + * history into segments of approximately 1ms (1024us); label the segment that > + * occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g. > + * > + * [<- 1024us ->|<- 1024us ->|<- 1024us ->| ... > + * p0 p1 p1 p2 > + * (now) (~1ms ago) (~2ms ago) > + * > + * Let u_i denote the fraction of p_i that the entity was runnable. > + * > + * We then designate the fractions u_i as our co-efficients, yielding the > + * following representation of historical load: > + * u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ... > + * > + * We choose y based on the with of a reasonably scheduling period, fixing: width ? > + * y^32 = 0.5 > + * > + * This means that the contribution to load ~32ms ago (u_32) will be weighted > + * approximately half as much as the contribution to load within the last ms > + * (u_0). > + * > + * When a period "rolls over" and we have new u_0`, multiplying the previous > + * sum again by y is sufficient to update: > + * load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... ) > + * = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1] u_{i+1}] > + */ > +static __always_inline int __update_entity_runnable_avg(u64 now, Is the return value used by elsewhere? Thanks, Namhyung > + struct sched_avg *sa, > + int runnable) > +{ > + u64 delta; > + int delta_w, decayed = 0; > + > + delta = now - sa->last_runnable_update; > + /* > + * This should only happen when time goes backwards, which it > + * unfortunately does during sched clock init when we swap over to TSC. > + */ > + if ((s64)delta < 0) { > + sa->last_runnable_update = now; > + return 0; > + } > + > + /* > + * Use 1024ns as the unit of measurement since it's a reasonable > + * approximation of 1us and fast to compute. > + */ > + delta >>= 10; > + if (!delta) > + return 0; > + sa->last_runnable_update = now; > + > + /* delta_w is the amount already accumulated against our next period */ > + delta_w = sa->runnable_avg_period % 1024; > + if (delta + delta_w >= 1024) { > + /* period roll-over */ > + decayed = 1; > + > + /* > + * Now that we know we're crossing a period boundary, figure > + * out how much from delta we need to complete the current > + * period and accrue it. > + */ > + delta_w = 1024 - delta_w; > + BUG_ON(delta_w > delta); > + do { > + if (runnable) > + sa->runnable_avg_sum += delta_w; > + sa->runnable_avg_period += delta_w; > + > + /* > + * Remainder of delta initiates a new period, roll over > + * the previous. > + */ > + sa->runnable_avg_sum = > + decay_load(sa->runnable_avg_sum, 1); > + sa->runnable_avg_period = > + decay_load(sa->runnable_avg_period, 1); > + > + delta -= delta_w; > + /* New period is empty */ > + delta_w = 1024; > + } while (delta >= 1024); > + } > + > + /* Remainder of delta accrued against u_0` */ > + if (runnable) > + sa->runnable_avg_sum += delta; > + sa->runnable_avg_period += delta; > + > + return decayed; > +} > + > +/* Update a sched_entity's runnable average */ > +static inline void update_entity_load_avg(struct sched_entity *se) > +{ > + __update_entity_runnable_avg(rq_of(cfs_rq_of(se))->clock_task, &se->avg, > + se->on_rq); > +} > +#else > +static inline void update_entity_load_avg(struct sched_entity *se) {} > +#endif > + > static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se) > { > #ifdef CONFIG_SCHEDSTATS > @@ -1102,6 +1221,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > */ > update_curr(cfs_rq); > update_cfs_load(cfs_rq, 0); > + update_entity_load_avg(se); > account_entity_enqueue(cfs_rq, se); > update_cfs_shares(cfs_rq); > > @@ -1176,6 +1296,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > * Update run-time statistics of the 'current'. > */ > update_curr(cfs_rq); > + update_entity_load_avg(se); > > update_stats_dequeue(cfs_rq, se); > if (flags & DEQUEUE_SLEEP) { > @@ -1345,6 +1466,8 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev) > update_stats_wait_start(cfs_rq, prev); > /* Put 'current' back into the tree. */ > __enqueue_entity(cfs_rq, prev); > + /* in !on_rq case, update occurred at dequeue */ > + update_entity_load_avg(prev); > } > cfs_rq->curr = NULL; > } > @@ -1358,6 +1481,11 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued) > update_curr(cfs_rq); > > /* > + * Ensure that runnable average is periodically updated. > + */ > + update_entity_load_avg(curr); > + > + /* > * Update share accounting for long-running entities. > */ > update_entity_shares_tick(cfs_rq); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/