Subject: Re: volanoMark 12% regression with 2.6.25-rc6
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <20080319021555.GA15825@elte.hu>
References: <1205831650.3215.569.camel@ymzhang>
	 <20080318195807.GA26887@elte.hu> <1205892420.3215.594.camel@ymzhang>
	 <20080319021555.GA15825@elte.hu>
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Date: Wed, 19 Mar 2008 11:18:42 +0800
Message-Id: <1205896722.3215.624.camel@ymzhang>
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On Wed, 2008-03-19 at 03:15 +0100, Ingo Molnar wrote:
> * Zhang, Yanmin <yanmin_zhang@linux.intel.com> wrote:
> 
> > Could you send me a patch against 2.6.25-rc6? Or just send me the 
> > kernel/sched*.c?
> 
> sure - the jist of it should be in the patch below.
I did a quick test and didn't find much help with the new patch.

-yanmin

> 
> 	Ingo
> 
> ------------------>
> Ingo Molnar (8):
>       sched: clean up fair wakeup balancing
>       sched: clean up fair wakeup balancing, #2
>       sched: clean up fair wakeup balancing, #3
>       sched: net socket wakeups are sync
>       sched: improved affine wakeups
>       sched: wakeup-buddy tasks are cache-hot
>       sched: retune wake granularity
>       sched: tune multi-core idle balancing
> 
>  include/linux/sched.h    |    3 +
>  include/linux/topology.h |    1 -
>  kernel/sched.c           |   11 +++-
>  kernel/sched_debug.c     |    1 +
>  kernel/sched_fair.c      |  191 ++++++++++++++++++++++++++++------------------
>  net/core/sock.c          |    4 +-
>  6 files changed, 134 insertions(+), 77 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 11d8e9a..3625fca 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -929,6 +929,9 @@ struct sched_entity {
>  	u64			vruntime;
>  	u64			prev_sum_exec_runtime;
>  
> +	u64			last_wakeup;
> +	u64			avg_overlap;
> +
>  #ifdef CONFIG_SCHEDSTATS
>  	u64			wait_start;
>  	u64			wait_max;
> diff --git a/include/linux/topology.h b/include/linux/topology.h
> index 2352f46..2d8dac8 100644
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -138,7 +138,6 @@
>  				| SD_BALANCE_FORK	\
>  				| SD_BALANCE_EXEC	\
>  				| SD_WAKE_AFFINE	\
> -				| SD_WAKE_IDLE		\
>  				| SD_SHARE_PKG_RESOURCES\
>  				| BALANCE_FOR_MC_POWER,	\
>  	.last_balance		= jiffies,		\
> diff --git a/kernel/sched.c b/kernel/sched.c
> index d1ad69b..3f7c5eb 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1396,6 +1396,12 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
>  {
>  	s64 delta;
>  
> +	/*
> +	 * Buddy candidates are cache hot:
> +	 */
> +	if (&p->se == cfs_rq_of(&p->se)->next)
> +		return 1;
> +
>  	if (p->sched_class != &fair_sched_class)
>  		return 0;
>  
> @@ -1855,10 +1861,11 @@ out_activate:
>  		schedstat_inc(p, se.nr_wakeups_remote);
>  	update_rq_clock(rq);
>  	activate_task(rq, p, 1);
> -	check_preempt_curr(rq, p);
>  	success = 1;
>  
>  out_running:
> +	check_preempt_curr(rq, p);
> +
>  	p->state = TASK_RUNNING;
>  #ifdef CONFIG_SMP
>  	if (p->sched_class->task_wake_up)
> @@ -1892,6 +1899,8 @@ static void __sched_fork(struct task_struct *p)
>  	p->se.exec_start		= 0;
>  	p->se.sum_exec_runtime		= 0;
>  	p->se.prev_sum_exec_runtime	= 0;
> +	p->se.last_wakeup		= 0;
> +	p->se.avg_overlap		= 0;
>  
>  #ifdef CONFIG_SCHEDSTATS
>  	p->se.wait_start		= 0;
> diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
> index 4b5e24c..ef358ba 100644
> --- a/kernel/sched_debug.c
> +++ b/kernel/sched_debug.c
> @@ -288,6 +288,7 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
>  	PN(se.exec_start);
>  	PN(se.vruntime);
>  	PN(se.sum_exec_runtime);
> +	PN(se.avg_overlap);
>  
>  	nr_switches = p->nvcsw + p->nivcsw;
>  
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index f2cc590..b85cac4 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -73,13 +73,13 @@ unsigned int sysctl_sched_batch_wakeup_granularity = 10000000UL;
>  
>  /*
>   * SCHED_OTHER wake-up granularity.
> - * (default: 10 msec * (1 + ilog(ncpus)), units: nanoseconds)
> + * (default: 5 msec * (1 + ilog(ncpus)), units: nanoseconds)
>   *
>   * This option delays the preemption effects of decoupled workloads
>   * and reduces their over-scheduling. Synchronous workloads will still
>   * have immediate wakeup/sleep latencies.
>   */
> -unsigned int sysctl_sched_wakeup_granularity = 10000000UL;
> +unsigned int sysctl_sched_wakeup_granularity = 5000000UL;
>  
>  const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
>  
> @@ -556,6 +556,21 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
>  	account_entity_enqueue(cfs_rq, se);
>  }
>  
> +static void update_avg(u64 *avg, u64 sample)
> +{
> +	s64 diff = sample - *avg;
> +	*avg += diff >> 3;
> +}
> +
> +static void update_avg_stats(struct cfs_rq *cfs_rq, struct sched_entity *se)
> +{
> +	if (!se->last_wakeup)
> +		return;
> +
> +	update_avg(&se->avg_overlap, se->sum_exec_runtime - se->last_wakeup);
> +	se->last_wakeup = 0;
> +}
> +
>  static void
>  dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
>  {
> @@ -566,6 +581,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
>  
>  	update_stats_dequeue(cfs_rq, se);
>  	if (sleep) {
> +		update_avg_stats(cfs_rq, se);
>  #ifdef CONFIG_SCHEDSTATS
>  		if (entity_is_task(se)) {
>  			struct task_struct *tsk = task_of(se);
> @@ -980,96 +996,121 @@ static inline int wake_idle(int cpu, struct task_struct *p)
>  #endif
>  
>  #ifdef CONFIG_SMP
> -static int select_task_rq_fair(struct task_struct *p, int sync)
> +
> +static const struct sched_class fair_sched_class;
> +
> +static int
> +wake_affine(struct rq *rq, struct sched_domain *this_sd, struct rq *this_rq,
> +	    struct task_struct *p, int prev_cpu, int this_cpu, int sync,
> +	    int idx, unsigned long load, unsigned long this_load,
> +	    unsigned int imbalance)
>  {
> -	int cpu, this_cpu;
> -	struct rq *rq;
> -	struct sched_domain *sd, *this_sd = NULL;
> -	int new_cpu;
> +	struct task_struct *curr = this_rq->curr;
> +	unsigned long tl = this_load;
> +	unsigned long tl_per_task;
> +
> +	if (!(this_sd->flags & SD_WAKE_AFFINE))
> +		return 0;
> +
> +	/*
> +	 * If the currently running task will sleep within
> +	 * a reasonable amount of time then attract this newly
> +	 * woken task:
> +	 */
> +	if (sync && curr->sched_class == &fair_sched_class) {
> +		if (curr->se.avg_overlap < sysctl_sched_migration_cost &&
> +				p->se.avg_overlap < sysctl_sched_migration_cost)
> +			return 1;
> +	}
>  
> -	cpu      = task_cpu(p);
> -	rq       = task_rq(p);
> -	this_cpu = smp_processor_id();
> -	new_cpu  = cpu;
> +	schedstat_inc(p, se.nr_wakeups_affine_attempts);
> +	tl_per_task = cpu_avg_load_per_task(this_cpu);
>  
> -	if (cpu == this_cpu)
> -		goto out_set_cpu;
> +	/*
> +	 * If sync wakeup then subtract the (maximum possible)
> +	 * effect of the currently running task from the load
> +	 * of the current CPU:
> +	 */
> +	if (sync)
> +		tl -= current->se.load.weight;
> +
> +	if ((tl <= load && tl + target_load(prev_cpu, idx) <= tl_per_task) ||
> +			100*(tl + p->se.load.weight) <= imbalance*load) {
> +		/*
> +		 * This domain has SD_WAKE_AFFINE and
> +		 * p is cache cold in this domain, and
> +		 * there is no bad imbalance.
> +		 */
> +		schedstat_inc(this_sd, ttwu_move_affine);
> +		schedstat_inc(p, se.nr_wakeups_affine);
>  
> +		return 1;
> +	}
> +	return 0;
> +}
> +
> +static int select_task_rq_fair(struct task_struct *p, int sync)
> +{
> +	struct sched_domain *sd, *this_sd = NULL;
> +	int prev_cpu, this_cpu, new_cpu;
> +	unsigned long load, this_load;
> +	struct rq *rq, *this_rq;
> +	unsigned int imbalance;
> +	int idx;
> +
> +	prev_cpu	= task_cpu(p);
> +	rq		= task_rq(p);
> +	this_cpu	= smp_processor_id();
> +	this_rq		= cpu_rq(this_cpu);
> +	new_cpu		= prev_cpu;
> +
> +	/*
> +	 * 'this_sd' is the first domain that both
> +	 * this_cpu and prev_cpu are present in:
> +	 */
>  	for_each_domain(this_cpu, sd) {
> -		if (cpu_isset(cpu, sd->span)) {
> +		if (cpu_isset(prev_cpu, sd->span)) {
>  			this_sd = sd;
>  			break;
>  		}
>  	}
>  
>  	if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
> -		goto out_set_cpu;
> +		goto out;
>  
>  	/*
>  	 * Check for affine wakeup and passive balancing possibilities.
>  	 */
> -	if (this_sd) {
> -		int idx = this_sd->wake_idx;
> -		unsigned int imbalance;
> -		unsigned long load, this_load;
> -
> -		imbalance = 100 + (this_sd->imbalance_pct - 100) / 2;
> -
> -		load = source_load(cpu, idx);
> -		this_load = target_load(this_cpu, idx);
> -
> -		new_cpu = this_cpu; /* Wake to this CPU if we can */
> -
> -		if (this_sd->flags & SD_WAKE_AFFINE) {
> -			unsigned long tl = this_load;
> -			unsigned long tl_per_task;
> -
> -			/*
> -			 * Attract cache-cold tasks on sync wakeups:
> -			 */
> -			if (sync && !task_hot(p, rq->clock, this_sd))
> -				goto out_set_cpu;
> -
> -			schedstat_inc(p, se.nr_wakeups_affine_attempts);
> -			tl_per_task = cpu_avg_load_per_task(this_cpu);
> -
> -			/*
> -			 * If sync wakeup then subtract the (maximum possible)
> -			 * effect of the currently running task from the load
> -			 * of the current CPU:
> -			 */
> -			if (sync)
> -				tl -= current->se.load.weight;
> -
> -			if ((tl <= load &&
> -				tl + target_load(cpu, idx) <= tl_per_task) ||
> -			       100*(tl + p->se.load.weight) <= imbalance*load) {
> -				/*
> -				 * This domain has SD_WAKE_AFFINE and
> -				 * p is cache cold in this domain, and
> -				 * there is no bad imbalance.
> -				 */
> -				schedstat_inc(this_sd, ttwu_move_affine);
> -				schedstat_inc(p, se.nr_wakeups_affine);
> -				goto out_set_cpu;
> -			}
> -		}
> +	if (!this_sd)
> +		goto out;
>  
> -		/*
> -		 * Start passive balancing when half the imbalance_pct
> -		 * limit is reached.
> -		 */
> -		if (this_sd->flags & SD_WAKE_BALANCE) {
> -			if (imbalance*this_load <= 100*load) {
> -				schedstat_inc(this_sd, ttwu_move_balance);
> -				schedstat_inc(p, se.nr_wakeups_passive);
> -				goto out_set_cpu;
> -			}
> +	idx = this_sd->wake_idx;
> +
> +	imbalance = 100 + (this_sd->imbalance_pct - 100) / 2;
> +
> +	load = source_load(prev_cpu, idx);
> +	this_load = target_load(this_cpu, idx);
> +
> +	if (wake_affine(rq, this_sd, this_rq, p, prev_cpu, this_cpu, sync, idx,
> +				     load, this_load, imbalance))
> +		return this_cpu;
> +
> +	if (prev_cpu == this_cpu)
> +		goto out;
> +
> +	/*
> +	 * Start passive balancing when half the imbalance_pct
> +	 * limit is reached.
> +	 */
> +	if (this_sd->flags & SD_WAKE_BALANCE) {
> +		if (imbalance*this_load <= 100*load) {
> +			schedstat_inc(this_sd, ttwu_move_balance);
> +			schedstat_inc(p, se.nr_wakeups_passive);
> +			return this_cpu;
>  		}
>  	}
>  
> -	new_cpu = cpu; /* Could not wake to this_cpu. Wake to cpu instead */
> -out_set_cpu:
> +out:
>  	return wake_idle(new_cpu, p);
>  }
>  #endif /* CONFIG_SMP */
> @@ -1092,6 +1133,10 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
>  		return;
>  	}
>  
> +	se->last_wakeup = se->sum_exec_runtime;
> +	if (unlikely(se == pse))
> +		return;
> +
>  	cfs_rq_of(pse)->next = pse;
>  
>  	/*
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 09cb3a7..2654c14 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1621,7 +1621,7 @@ static void sock_def_readable(struct sock *sk, int len)
>  {
>  	read_lock(&sk->sk_callback_lock);
>  	if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> -		wake_up_interruptible(sk->sk_sleep);
> +		wake_up_interruptible_sync(sk->sk_sleep);
>  	sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
>  	read_unlock(&sk->sk_callback_lock);
>  }
> @@ -1635,7 +1635,7 @@ static void sock_def_write_space(struct sock *sk)
>  	 */
>  	if ((atomic_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf) {
>  		if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> -			wake_up_interruptible(sk->sk_sleep);
> +			wake_up_interruptible_sync(sk->sk_sleep);
>  
>  		/* Should agree with poll, otherwise some programs break */
>  		if (sock_writeable(sk))

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