Messages in this thread | | | Date | Wed, 20 Jan 2010 17:35:19 +0900 | From | Tejun Heo <> | Subject | Re: [PATCH 04/40] sched: implement __set_cpus_allowed() |
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Hello,
On 01/19/2010 05:37 PM, Peter Zijlstra wrote: > On Tue, 2010-01-19 at 10:07 +0900, Tejun Heo wrote: >> >> It's also necessary to guarantee forward progress during CPU_DOWN. >> The problem with kthread_bind() is that it's not synchronized against >> CPU hotplug operations. It needs outer synchronization like calling >> it directly from CPU_DOWN_PREP. I guess it's doable but I think it >> would be better to simply share the backend implementation between >> set_cpus_allowed_ptr() and kthread_bind(). > > OK, so you're saying you need to migrate the rescue thread during > cpu-down. That thread is guaranteed sleeping right,
No, it's not. It might have been tasked to process works from other CPUs.
> if it were not it'd not be elegible to run on our dying cpu. Hence > kthread_bind() ought to just work, no?
Why wouldn't it be elegible?
Commit e2912009fb7b715728311b0d8fe327a1432b3f79 killed the ability to bind a kthread to a dead CPU which means that the only differences between kthread_bind() and set_cpus_allowed_ptr() are...
* Whether to use cpu_online_mask or cpu_active_mask.
* Whether to set or check PF_THREAD_BOUND.
Wouldn't it make more sense to share the backend implementation between kthread_bind() and set_cpus_allowed_ptr() instead of making kthread_bind() a special case? The goals of the two functions are basically identical. Why have two separate implementations? kthread_bind() implementation as it currently stands is pretty fragile too. Making kthread_bind() backed by set_cpus_allowed_ptr() will make it more robust and less error-prone and all that's necessary to achieve that is modifying sanity checks.
Thanks.
-- tejun
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