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List:       linux-driver-devel
Subject:    Re: [PATCH 1/2] staging: octeon-ethernet: don't assume that CPU 0 is special
From:       Aaro Koskinen <aaro.koskinen () iki ! fi>
Date:       2013-09-30 21:27:08
Message-ID: 20130930212707.GA14359 () blackmetal ! musicnaut ! iki ! fi
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Hi,

On Mon, Sep 30, 2013 at 02:08:31PM -0700, David Daney wrote:
> On 09/30/2013 12:56 PM, Aaro Koskinen wrote:
> >What guarantees that CPU0 is around (or the smp_affinity is at its
> >default value) by the time user executes modprobe?
> 
> Nothing enforced by the kernel.  Just don't take CPU0 off-line and
> you should be good to go.
> 
> There is a lot of room for improvement in the driver.
> 
> Really this whole thing of starting NAPI on multiple CPUs for the
> same input queue is not good.  It leads to loss of packet ordering
> when forwarding.

I agree. I have also another patch which deletes this functionality
altogether - should I post that one instead? In modern kernel you can use
RPS to steer packets to different cores/softirqs threads, so in a way the
driver currently duplicates some of the generic kernel functionality...

A.
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