linux-kernel - Re: [PATCH v6] x86/apic: limit irq affinity

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Date:	Mon, 7 Dec 2009 07:44:48 -0600
From:	Dimitri Sivanich <sivanich@....com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	David Miller <davem@...emloft.net>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v6] x86/apic: limit irq affinity

On Fri, Dec 04, 2009 at 03:12:14PM -0800, Eric W. Biederman wrote:
> Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com> writes:
> 
> >> > > As a matter of fact, driver's allocating rings, buffers, queues on other nodes should optimally be made aware of the restriction.
> >> > 
> >> > The idea is that the driver will do its memory allocations for everything 
> >> > across nodes.  When it does that, it will use the kernel interface 
> >> > (function call) to set the corresponding mask it wants for those queue 
> >> > resources.  That is my end-goal for this code.
> >> > 
> >> 
> >> OK, but we will eventually have to reject any irqbalance attempts to send irqs to restricted nodes.
> >
> > See above.
> 
> Either I am parsing this conversation wrong or there is a strong
> reality distortion field in place.  It appears you are asking that we
> depend on a user space application to not attempt the physically
> impossible, when we could just as easily ignore or report -EINVAL to.
> 
> We really have two separate problems hear.
> - How to avoid the impossible.

The kernel does need to restrict attempts at the impossible.  However I see
nothing wrong with providing apps with information as to what the impossible
actually is.

> - How to deal with NUMA affinity.
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