Re: [PATCH v2 3/4] kthread: NUMA aware kthread_create_on_cpu()

Eric Dumazet
2010-12-10T05:59:58Z

Le jeudi 09 décembre 2010 à 16:44 -0800, Andrew Morton a écrit :

> 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 :)