Messages in this thread | | | Date | Mon, 26 Nov 2012 14:32:49 -0800 | From | Tejun Heo <> | Subject | Why is cpuset_cpus_allowed_fallback() necessary? |
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Hello, guys.
I'm wondering why cpuset_cpus_allowed_fallback() is necessary. This is called from, e.g., try_to_wake_up()->select_task_rq() when none of the cpus in ->cpus_allowed is useable. The cpuset callback invokes do_set_cpus_allowed() w/ the cpuset's cpus_allowed. This was added by the following commit,
commit 9084bb8246ea935b98320554229e2f371f7f52fa Author: Oleg Nesterov <oleg@redhat.com> Date: Mon Mar 15 10:10:27 2010 +0100
sched: Make select_fallback_rq() cpuset friendly
Introduce cpuset_cpus_allowed_fallback() helper to fix the cpuset problems with select_fallback_rq(). It can be called from any context and can't use any cpuset locks including task_lock(). It is called when the task doesn't have online cpus in ->cpus_allowed but ttwu/etc must be able to find a suitable cpu. ....
The problem is, nothing's explaining what "the cpuset problems with select_fallback_rq()" are. Oleg, do you remember? Why do we need this?
Thanks.
-- tejun
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