Messages in this thread | | | Date | Tue, 29 May 2012 18:11:57 +0200 | From | Andrea Arcangeli <> | Subject | Re: [PATCH 08/35] autonuma: introduce kthread_bind_node() |
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On Tue, May 29, 2012 at 02:49:13PM +0200, Peter Zijlstra wrote: > On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote: > > /** > > + * kthread_bind_node - bind a just-created kthread to the CPUs of a node. > > + * @p: thread created by kthread_create(). > > + * @nid: node (might not be online, must be possible) for @k to run on. > > + * > > + * Description: This function is equivalent to set_cpus_allowed(), > > + * except that @nid doesn't need to be online, and the thread must be > > + * stopped (i.e., just returned from kthread_create()). > > + */ > > +void kthread_bind_node(struct task_struct *p, int nid) > > +{ > > + /* Must have done schedule() in kthread() before we set_task_cpu */ > > + if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) { > > + WARN_ON(1); > > + return; > > + } > > + > > + /* It's safe because the task is inactive. */ > > + do_set_cpus_allowed(p, cpumask_of_node(nid)); > > + p->flags |= PF_THREAD_BOUND; > > No, I've said before, this is wrong. You should only ever use > PF_THREAD_BOUND when its strictly per-cpu. Moving the your numa threads > to a different node is silly but not fatal in any way.
I changed the semantics of that bitflag, now it means: userland isn't allowed to shoot itself in the foot and mess with whatever CPU bindings the kernel has set for the kernel thread.
It'd be a clear regress not to set PF_THREAD_BOUND there. It would be even worse to remove the CPU binding to the node: it'd risk to copy memory with both src and dst being in remote nodes from the CPU where knuma_migrate runs on (there aren't just 2 node systems out there).
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