netdev - Re: [net-next-2.6 PATCH 2/5] ixgbe: Make descriptor ring allocations NUMA-aware

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Date:	Fri, 8 Jan 2010 00:25:26 -0800 (Pacific Standard Time)
From:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
To:	David Miller <davem@...emloft.net>
cc:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
Subject: Re: [net-next-2.6 PATCH 2/5] ixgbe: Make descriptor ring allocations
 NUMA-aware

On Fri, 8 Jan 2010, David Miller wrote:

> From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> Date: Wed, 06 Jan 2010 20:48:46 -0800
> 
> > @@ -147,7 +147,7 @@ struct ixgbe_ring {
> >  
> >  #ifdef CONFIG_IXGBE_DCA
> >  	/* cpu for tx queue */
> > -	int cpu;
> > +	u8 cpu;
> >  #endif
> >  
> >  	u16 work_limit;			/* max work per interrupt */
> 
> Is truncating cpu and node numbers to 8-bits ok?  I really don't
> see how it can be fine, even for DCA.

In our hardware (82598 and 82599), the CPU field in the DCA registers is 8 
bits.

The reason I truncated this was to fit these values into the 
first cacheline of the struct.  I also didn't figure we'd see a system 
that would have 255 NUMA nodes before 10 GbE was something that was on the 
shelf collecting dust.  :-)

> This is especially the case since dca3_get_tag() and the
> DCA ->get_tag() callback explicitly take an 'int' argument
> too.

Cheers,
-PJ
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