linux-kernel - Re: [PATCH RFC: linux-next 1/2] irq: Add CPU mask affinity hint callback framework

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Date:	Thu, 29 Apr 2010 14:29:10 -0700
From:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"arjan@...ux.jf.intel.com" <arjan@...ux.jf.intel.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC: linux-next 1/2] irq: Add CPU mask affinity hint
 callback framework

On Thu, 2010-04-29 at 13:39 -0700, Thomas Gleixner wrote:
> On Thu, 29 Apr 2010, Peter P Waskiewicz Jr wrote:
> > On Thu, 2010-04-29 at 12:48 -0700, Thomas Gleixner wrote:
> > > Thinking more about it, I wonder whether you have a cpu_mask in your
> > > driver/device private data anyway. I bet you have :)
> > 
> > Well, at this point we don't, but nothing says we can't.
> 
> Somewhere you need to store that information in your driver, right ?

Yes.  But right now, storing a cpu_mask for an interrupt wouldn't buy us
anything since we have no mechanism to make use of it today.  :-)

I'll be putting the cpu_mask entry in our q_vector structure, which is
our abstraction of the MSI-X vector (it's where I have the hint struct
right now in patch 2/2 for the ixgbe driver).  It's a simple place to
stick it.

> > > So it should be sufficient to set a pointer to that cpu_mask in
> > > irq_desc and get rid of the callback completely.
> > 
> > So "register" would just assign the pointer, and "unregister" would make
> > sure to NULL the mask pointer out.  I like it.  It'll sure clean things
> > up too.
> 
> Yep, that'd be like the set_irq_chip() function. Just assign the
> pointer under desc->lock.
> 
> Thanks,
> 
> 	tglx


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