On 10/3/07, Paul Jackson <[email protected]> wrote:
>
> Yes, something in user space has to do it. It's part of the
> kernel-user cpuset API. If you change a cpuset's 'cpus', then
> you have to rewrite each pid in its 'tasks' file back to that
> 'tasks' file in order to get that 'cpus' change to be applied
> to the task struct cpus_allowed of each task, and thereby visible
> to the scheduler.
What's the rationale for this?
Given that later in cpusets.txt you say:
>If hotplug functionality is used
>to remove all the CPUs that are currently assigned to a cpuset,
>then the kernel will automatically update the cpus_allowed of all
>tasks attached to CPUs in that cpuset to allow all CPUs
why can't the same thing be done when changing the 'cpus' file manually.
What's wrong with, in update_cpumask(), doing a loop across all
members of the cgroup and updating their cpus_allowed fields?
The existing cpusets API is broken, since a new child can always be
forked between reading the tasks file and doing the writes.
Paul
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