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Message-ID: <CAPM31R+cS+eRaFHa2ygxF3ADYyo5Tf9R+snky3U8b5_am6Wtjg@mail.gmail.com>
Date: Wed, 13 Jul 2011 10:13:08 -0700
From: Paul Turner <pjt@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Nikhil Rao <ncrao@...gle.com>,
Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...e.hu>, Mike Galbraith <efault@....de>
Subject: Re: [RFT][PATCH] sched, cgroup: Optimize load_balance_fair()
Nice! The continued usage of task_groups had been irking me for a
while but I haven't had the time to scratch the itch :).
On Wed, Jul 13, 2011 at 4:36 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> Subject: sched, cgroup: Optimize load_balance_fair()
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Wed Jul 13 13:09:25 CEST 2011
>
> Use for_each_leaf_cfs_rq() instead of list_for_each_entry_rcu(), this
> achieves that load_balance_fair() only iterates those task_groups that
> actually have tasks on busiest, and that we iterate bottom-up, trying to
> move light groups before the heavier ones.
>
> No idea if it will actually work out to be beneficial in practice, does
> anybody have a cgroup workload that might show a difference one way or
> the other?
>
> [ Also move update_h_load to sched_fair.c, loosing #ifdef-ery ]
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> kernel/sched.c | 32 --------------------------------
> kernel/sched_fair.c | 40 +++++++++++++++++++++++++++++++++++-----
> 2 files changed, 35 insertions(+), 37 deletions(-)
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -1568,38 +1568,6 @@ static unsigned long cpu_avg_load_per_ta
> return rq->avg_load_per_task;
> }
>
> -#ifdef CONFIG_FAIR_GROUP_SCHED
> -
> -/*
> - * Compute the cpu's hierarchical load factor for each task group.
> - * This needs to be done in a top-down fashion because the load of a child
> - * group is a fraction of its parents load.
> - */
> -static int tg_load_down(struct task_group *tg, void *data)
> -{
> - unsigned long load;
> - long cpu = (long)data;
> -
> - if (!tg->parent) {
> - load = cpu_rq(cpu)->load.weight;
> - } else {
> - load = tg->parent->cfs_rq[cpu]->h_load;
> - load *= tg->se[cpu]->load.weight;
> - load /= tg->parent->cfs_rq[cpu]->load.weight + 1;
> - }
> -
> - tg->cfs_rq[cpu]->h_load = load;
> -
> - return 0;
> -}
> -
> -static void update_h_load(long cpu)
> -{
> - walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);
> -}
> -
> -#endif
> -
> #ifdef CONFIG_PREEMPT
>
> static void double_rq_lock(struct rq *rq1, struct rq *rq2);
> Index: linux-2.6/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_fair.c
> +++ linux-2.6/kernel/sched_fair.c
> @@ -2232,11 +2232,43 @@ static void update_shares(int cpu)
> struct rq *rq = cpu_rq(cpu);
>
> rcu_read_lock();
> + /*
> + * Iterates the task_group tree in a bottom up fashion, see
> + * list_add_leaf_cfs_rq() for details.
> + */
> for_each_leaf_cfs_rq(rq, cfs_rq)
> update_shares_cpu(cfs_rq->tg, cpu);
> rcu_read_unlock();
> }
>
> +/*
> + * Compute the cpu's hierarchical load factor for each task group.
> + * This needs to be done in a top-down fashion because the load of a child
> + * group is a fraction of its parents load.
> + */
> +static int tg_load_down(struct task_group *tg, void *data)
> +{
> + unsigned long load;
> + long cpu = (long)data;
> +
> + if (!tg->parent) {
> + load = cpu_rq(cpu)->load.weight;
> + } else {
> + load = tg->parent->cfs_rq[cpu]->h_load;
> + load *= tg->se[cpu]->load.weight;
> + load /= tg->parent->cfs_rq[cpu]->load.weight + 1;
> + }
> +
> + tg->cfs_rq[cpu]->h_load = load;
> +
> + return 0;
> +}
> +
> +static void update_h_load(long cpu)
> +{
> + walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);
> +}
With a list_for_each_entry_reverse_rcu() this could also only operate
on the local hierarchy and avoid the tg tree walk.
> +
> static unsigned long
> load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
> unsigned long max_load_move,
> @@ -2244,14 +2276,12 @@ load_balance_fair(struct rq *this_rq, in
> int *all_pinned)
> {
> long rem_load_move = max_load_move;
> - int busiest_cpu = cpu_of(busiest);
> - struct task_group *tg;
> + struct cfs_rq *busiest_cfs_rq;
>
> rcu_read_lock();
> - update_h_load(busiest_cpu);
> + update_h_load(cpu_of(busiest));
>
> - list_for_each_entry_rcu(tg, &task_groups, list) {
> - struct cfs_rq *busiest_cfs_rq = tg->cfs_rq[busiest_cpu];
> + for_each_leaf_cfs_rq(busiest, busiest_cfs_rq) {
> unsigned long busiest_h_load = busiest_cfs_rq->h_load;
> unsigned long busiest_weight = busiest_cfs_rq->load.weight;
> u64 rem_load, moved_load;
>
>
Reviewed-by: Paul Turner <pjt@...gle.com>
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