Messages in this thread | | | Subject | Re: [PATCH v3 09/14] sched/core: uclamp: propagate parent clamps | From | Dietmar Eggemann <> | Date | Fri, 17 Aug 2018 15:43:59 +0200 |
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On 08/06/2018 06:39 PM, Patrick Bellasi 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.
I don't understand the reason mentioned here:
IMHO, a write to a child's (tg1/tg11) cpu.rt_runtime_us can fail if the value is restricted by the parents value:
root@juno:/sys/fs/cgroup/cpu# cat cpu.rt_* 1000000 950000 root@juno:/sys/fs/cgroup/cpu# cat tg1/cpu.rt_* 1000000 0 root@juno:/sys/fs/cgroup/cpu# cat tg1/tg11/cpu.rt_* 1000000 0 root@juno:/sys/fs/cgroup/cpu# echo 950000 > tg1/tg11/cpu.rt_runtime_us -bash: echo: write error: Invalid argument root@juno:/sys/fs/cgroup/cpu# echo 950000 > tg1/cpu.rt_runtime_us root@juno:/sys/fs/cgroup/cpu# echo 950000 > tg1/tg11/cpu.rt_runtime_us root@juno:/sys/fs/cgroup/cpu#
> 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 represent also the clamp value which is actually > used to clamp tasks in each task group. > > Since it can be interesting for tasks in a cgroup to know exactly what > is the currently propagated/enforced configuration, the effective clamp > values are exposed to user-space by means of a new pair of read-only > attributes: cpu.util.{min,max}.effective.
I assume here that the cpu.util.{min,max} of the child will not be used any more because the 'effective' counterparts are taken instead.
I wonder if this propagation not been provided with only cpu.util.{min,max}?
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