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SubjectRe: [patch 10/15] sched: allow for positional tg_tree walks
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On Tue, 2011-05-03 at 02:28 -0700, Paul Turner wrote:
> plain text document attachment (sched-bwc-refactor-walk_tg_tree.patch)
> Extend walk_tg_tree to accept a positional argument
>
> static int walk_tg_tree_from(struct task_group *from,
> tg_visitor down, tg_visitor up, void *data)
>
> Existing semantics are preserved, caller must hold rcu_lock() or sufficient
> analogue.
>
> Signed-off-by: Paul Turner <pjt@google.com>
> ---
> kernel/sched.c | 34 +++++++++++++++++++++++-----------
> 1 file changed, 23 insertions(+), 11 deletions(-)
>
> Index: tip/kernel/sched.c
> ===================================================================
> --- tip.orig/kernel/sched.c
> +++ tip/kernel/sched.c
> @@ -1430,21 +1430,19 @@ static inline void dec_cpu_load(struct r
> #if (defined(CONFIG_SMP) && defined(CONFIG_FAIR_GROUP_SCHED)) || defined(CONFIG_RT_GROUP_SCHED)
> typedef int (*tg_visitor)(struct task_group *, void *);
>
> -/*
> - * Iterate the full tree, calling @down when first entering a node and @up when
> - * leaving it for the final time.
> - */
> -static int walk_tg_tree(tg_visitor down, tg_visitor up, void *data)
> +/* Iterate task_group tree rooted at *from */
> +static int walk_tg_tree_from(struct task_group *from,
> + tg_visitor down, tg_visitor up, void *data)
> {
> struct task_group *parent, *child;
> int ret;
>
> - rcu_read_lock();
> - parent = &root_task_group;
> + parent = from;
> +
> down:
> ret = (*down)(parent, data);
> if (ret)
> - goto out_unlock;
> + goto out;
> list_for_each_entry_rcu(child, &parent->children, siblings) {
> parent = child;
> goto down;
> @@ -1453,14 +1451,28 @@ up:
> continue;
> }
> ret = (*up)(parent, data);
> - if (ret)
> - goto out_unlock;
> + if (ret || parent == from)
> + goto out;
>
> child = parent;
> parent = parent->parent;
> if (parent)
> goto up;
> -out_unlock:
> +out:
> + return ret;
> +}
> +
> +/*
> + * Iterate the full tree, calling @down when first entering a node and @up when
> + * leaving it for the final time.
> + */
> +
> +static inline int walk_tg_tree(tg_visitor down, tg_visitor up, void *data)
> +{
> + int ret;
> +
> + rcu_read_lock();
> + ret = walk_tg_tree_from(&root_task_group, down, up, data);
> rcu_read_unlock();
>
> return ret;

I don't much like the different locking rules for these two functions. I
don't much care which you pick, but please make them consistent.



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