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    SubjectRe: [PATCH v2 3/4] kthread: NUMA aware kthread_create_on_cpu()
    On Fri, 10 Dec 2010 06:59:58 +0100 Eric Dumazet <eric.dumazet@gmail.com> wrote:

    > Le jeudi 09 d__cembre 2010 __ 16:44 -0800, Andrew Morton a __crit :
    >
    > > The name "kthread_create_on_cpu" is pretty misleading.
    > >
    > > One would expect such a function to create a kthread which is bound to
    > > that CPU. But what it in fact does is to create a kthread which is
    > > bound to all CPUs and whose stack, task_struct and thread_info were
    > > allocated from the node which contains `cpu'.
    > >
    > > Also, a saner interface would be one which takes the numa_node_id, not
    > > the cpu number.
    > >
    >
    >
    > > >
    > > > ...
    > > >
    > > > /**
    > > > - * kthread_create - create a kthread.
    > > > + * kthread_create_on_cpu - create a kthread.
    > > > * @threadfn: the function to run until signal_pending(current).
    > > > * @data: data ptr for @threadfn.
    > > > + * @cpu: cpu number.
    > > > * @namefmt: printf-style name for the thread.
    > > > *
    > > > * Description: This helper function creates and names a kernel
    > > > * thread. The thread will be stopped: use wake_up_process() to start
    > > > * it. See also kthread_run().
    > > > *
    > > > + * If thread is going to be bound on a particular cpu, give its number
    > > > + * in @cpu, to get NUMA affinity for kthread stack, or else give -1.
    > >
    > > This is a bit presumptuous. The caller might wish to later bind this
    > > thread to some or all of the CPUs on the node, rather than to a single
    > > CPU (eg, kswapd()).
    > >
    > >
    > > So what to do? Maybe add a new kthread_create_node() which prepares a
    > > kthread whose memory is bound to that node, then add a
    > > kthread_create_cpu() convenience wrapper around that?
    > >
    >
    > We probably can add the "bind to cpu" as a fifth patch, to avoid one
    > kthread_bind(p, cpu); done by these callers.
    >
    > My reasoning not including this kthread_bind(p, cpu) in initial patch
    > series that I was focusing on NUMA properties first, not on scheduling
    > (this part already runs correctly as far as I know)
    >
    > Thanks for taking the patch series, I was about to resubmit it today :)
    >

    but but but. The name "kthread_create_on_cpu" sucks. It's plain wrong.


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