linux-kernel - Re: Fw: [PATCH] sunrpc: use better NUMA affinities

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Message-ID: <4E3258E1.6020000@fastmail.fm>
Date:	Fri, 29 Jul 2011 16:53:21 +1000
From:	Greg Banks <gnb@...tmail.fm>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	NeilBrown <neilb@...e.de>, linux-nfs@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Fw: [PATCH] sunrpc: use better NUMA affinities

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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