Subject: Re: [PATCH] irq: Add node_affinity CPU masks for smarter
 irqbalance hints
From: Peter Zijlstra <peterz@infradead.org>
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>,
       Yong Zhang <yong.zhang0@gmail.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "arjan@linux.jf.intel.com" <arjan@linux.jf.intel.com>,
       "davem@davemloft.net" <davem@davemloft.net>,
       "netdev@vger.kernel.org" <netdev@vger.kernel.org>
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Date: Tue, 24 Nov 2009 09:39:46 +0100
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On Mon, 2009-11-23 at 22:07 -0800, Arjan van de Ven wrote:
> Peter Zijlstra wrote:
> > On Mon, 2009-11-23 at 01:36 -0800, Peter P Waskiewicz Jr wrote:
> > 
> >> This mechanism isn't going to be used by any internal kernel mechanism
> >> for determining interrupt placement or operation.  It's purely something
> >> that either a driver can modify, or external script (through /proc),
> >> that irqbalance will make use of.  If irqbalance isn't running, or the
> >> current version of irqbalance doesn't support reading node_affinity,
> >> then it won't affect the system's operation.
> >>
> >> If irqbalance does support it, it'll read whatever the supplied mask is,
> >> and then will try and balance interrupts within that mask.  It will bail
> >> if the mask is invalid, or won't apply to the running system, just like
> >> how putting a bogus mask into smp_affinity is ignored.
> >>
> >> If there's something I'm missing beyond this with the two suggestions
> >> you've made (I looked into those two parameters and tried to draw
> >> conclusions), please let me know.
> > 
> > I don't see the point in adding it, if the driver wants to set a node
> > cpu mask it can already do that using the regular smp affinity settings.
> > 
> > Same for userspace.
> 
> the problem is that there is no way currently that the driver can communicate
> "I allocated all my metadata on THIS numa node". irqbalance and sysadmins need
> that to not make really stupid decisions.....

And what exactly is struct device::numa_node good for then?

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