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Date: Thu, 9 Dec 2010 16:44:38 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Andi Kleen <andi@...stfloor.org>, linux-kernel <linux-kernel@...r.kernel.org>, netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>, Tejun Heo <tj@...nel.org>, Rusty Russell <rusty@...tcorp.com.au>, Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com> Subject: Re: [PATCH v2 3/4] kthread: NUMA aware kthread_create_on_cpu() On Mon, 29 Nov 2010 16:14:55 +0100 Eric Dumazet <eric.dumazet@...il.com> wrote: > All kthreads being created from a single helper task, they all use > memory from a single node for their kernel stack and task struct. > > This patch suite creates kthread_create_on_cpu(), adding a 'cpu' > parameter to parameters already used by kthread_create(). > > This parameter serves in allocating memory for the new kthread on its > memory node if possible. 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? > > ... > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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