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Re: [PATCH 1/2] staging: octeon-ethernet: don't assume that CPU 0 is spe

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH 1/2] staging: octeon-ethernet: don't assume that CPU 0 is special
From: Aaro Koskinen <aaro.koskinen@iki.fi>
Date: Tue, 1 Oct 2013 00:27:08 +0300
Cc: devel@driverdev.osuosl.org, linux-mips@linux-mips.org, David Daney <david.daney@cavium.com>, richard@nod.at, Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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References: <1380397834-14286-1-git-send-email-aaro.koskinen@iki.fi> <5249B37E.4050000@caviumnetworks.com> <20130930193502.GE4572@blackmetal.musicnaut.iki.fi> <5249D407.2090904@caviumnetworks.com> <20130930195642.GF4572@blackmetal.musicnaut.iki.fi> <5249E84F.2070008@caviumnetworks.com>
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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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