On 14-Mar 09:17, Suren Baghdasaryan wrote:
> On Fri, Feb 8, 2019 at 2:06 AM Patrick Bellasi <patrick.bellasi@xxxxxxx> wrote:
> >
> > In order to properly support hierarchical resources control, the cgroup
> > delegation model requires that attribute writes from a child group never
> > fail but still are (potentially) constrained based on parent's assigned
> > resources. This requires to properly propagate and aggregate parent
> > attributes down to its descendants.
> >
> > Let's implement this mechanism by adding a new "effective" clamp value
> > for each task group. The effective clamp value is defined as the smaller
> > value between the clamp value of a group and the effective clamp value
> > of its parent. This is the actual clamp value enforced on tasks in a
> > task group.
>
> In patch 10 in this series you mentioned "b) do not enforce any
> constraints and/or dependencies between the parent and its child
> nodes"
>
> This patch seems to change that behavior. If so, should it be documented?
Not, I actually have to update the changelog of that patch.
What I mean is that we do not enforce constraints among "requested"
values thus ensuring that each sub-group can always request a clamp
value.
Of course, if it gets that value or not depends on parent constraints,
which are propagated down the hierarchy under the form of "effective"
values by cpu_util_update_heir()
I'll fix the changelog in patch 10 which seems to be confusing for
Tejun too.
[...]
> > @@ -7011,6 +7029,53 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
> > }
> >
> > #ifdef CONFIG_UCLAMP_TASK_GROUP
> > +static void cpu_util_update_hier(struct cgroup_subsys_state *css,
>
> s/cpu_util_update_hier/cpu_util_update_heir ?
Mmm... why?
That "_hier" stands for "hierarchical".
However, since there we update the effective values, maybe I can
better rename it in "_eff" ?
> > + unsigned int clamp_id, unsigned int bucket_id,
> > + unsigned int value)
> > +{
> > + struct cgroup_subsys_state *top_css = css;
> > + struct uclamp_se *uc_se, *uc_parent;
> > +
> > + css_for_each_descendant_pre(css, top_css) {
> > + /*
> > + * The first visited task group is top_css, which clamp value
> > + * is the one passed as parameter. For descendent task
> > + * groups we consider their current value.
> > + */
> > + uc_se = &css_tg(css)->uclamp[clamp_id];
> > + if (css != top_css) {
> > + value = uc_se->value;
> > + bucket_id = uc_se->effective.bucket_id;
> > + }
> > + uc_parent = NULL;
> > + if (css_tg(css)->parent)
> > + uc_parent = &css_tg(css)->parent->uclamp[clamp_id];
> > +
> > + /*
> > + * Skip the whole subtrees if the current effective clamp is
> > + * already matching the TG's clamp value.
> > + * In this case, all the subtrees already have top_value, or a
> > + * more restrictive value, as effective clamp.
> > + */
> > + if (uc_se->effective.value == value &&
> > + uc_parent && uc_parent->effective.value >= value) {
> > + css = css_rightmost_descendant(css);
> > + continue;
> > + }
> > +
> > + /* Propagate the most restrictive effective value */
> > + if (uc_parent && uc_parent->effective.value < value) {
> > + value = uc_parent->effective.value;
> > + bucket_id = uc_parent->effective.bucket_id;
> > + }
> > + if (uc_se->effective.value == value)
> > + continue;
> > +
> > + uc_se->effective.value = value;
> > + uc_se->effective.bucket_id = bucket_id;
> > + }
> > +}
> > +
> > static int cpu_util_min_write_u64(struct cgroup_subsys_state *css,
> > struct cftype *cftype, u64 min_value)
> > {
[...]
Cheers,
Patrick
--
#include <best/regards.h>
Patrick Bellasi
