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From: Sean Bruno <seanbru@yahoo-inc.com>
To: John Baldwin <jhb@freebsd.org>
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Date: Tue, 08 May 2012 21:36:05 -0700
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Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>,
	Jack Vogel <jfvogel@gmail.com>
Subject: Re: igb(4) Pondering a bind to cpu patch
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On Thu, 2012-05-03 at 15:33 -0700, Sean Bruno wrote:
> 
> On Wed, 2012-04-25 at 12:30 -0700, Sean Bruno wrote:
> > On Wed, 2012-04-25 at 06:32 -0700, John Baldwin wrote:
> > > CPU IDs are not guaranteed to be dense.  However, you can use
> > > CPU_FIRST() and 
> > > CPU_NEXT() with your static global instead.
> > > 
> > Ah, does CPU_NEXT() reset to 0 when it reaches the end of its list of
> > CPUs?
> > 
> 
> Ah, I see.  So, yeah, here's a v2 of the patch that does "the right"
> thing with non-sparse cpus, mulitple queues, and mulitple physical
> interfaces.
> 
> http://people.freebsd.org/~sbruno/if_igb.c.txt
> 
> > 
> > > OTOH, if igb were to just leave the interrupts alone instead of
> > > binding them 
> > > by hand, they would get round-robin assigned among available cores
> > > already.  I 
> > > think in this case the best approach might be to add a tunable to
> > > disable 
> > > igb's manual binding and instead let the default system round-robin
> > > be 
> > > preserved. 
> > 
> > also, yes.  Why *are* we binding to CPUs in the first place?  Are we
> > afraid that the scheduler won't do the right thing and we're trying to
> > work around some unknown performance issue ?
> > 
> > Sean
> > 
> 
> Still haven't seen a good reason to bind the queues by default in the
> first place.  
> 
> Sean
> 


If there's no objection, I'll commit this in the morning.

Sean