Re: Fw: [PATCH] sunrpc: use better NUMA affinities

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On 29/07/11 16:30, Eric Dumazet wrote:
Le vendredi 29 juillet 2011 à 16:05 +1000, Greg Banks a écrit :
On 29/07/11 15:32, NeilBrown wrote:

I seem to remember coming to the conclusion that Jeff eventually
addressed this problem...am I misremembering or did something regress?

Currently, all nfsd kthreads use memory for their kernel stack and
various initial data from a _single_ node, even if you use
sunrpc.pool_mode=pernode  (or percpu)

That's just plain broken and I'm very pleased to see you fix it.

I was just surprised that it was still broken and wondering how that happened. Looking at ToT I see that because I dropped the ball in 2008, Jeff's patches didn't address the problem. In ToT svc_pool_map_set_cpumask() is called *after* kthread_create() and applies to the child thread, *after* it's stack has been allocated on the wrong node. In the working SGI code, svc_pool_map_set_cpumask() is called by the parent node on itself *before* calling kernel_thread() or doing any of the data structure allocations, thus ensuring that everything gets allocated using the default memory allocation policy, which on SGI NFS servers was globally tuned to be "node-local".

With my patch, we make sure each thread gets its stack from its local
node.

Check commit 94dcf29a11b3d20a (kthread: use kthread_create_on_node()) to
see how this strategy already was adopted for ksoftirqd, kworker,
migration, and pktgend kthreads.

Ah, I see. It's unfortunate that the kthread_create() API ends up being passed a CPU number but that's only used to format the name and not for sensible things :(

--
Greg.

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