netdev - Re: [Intel-wired-lan] [net-next PATCH v3 2/3] e1000: add initial XDP support

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Date:   Wed, 14 Sep 2016 00:13:48 +0000
From:   "Rustad, Mark D" <mark.d.rustad@...el.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Eric Dumazet <eric.dumazet@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        "William Tu" <u9012063@...il.com>
Subject: Re: [Intel-wired-lan] [net-next PATCH v3 2/3] e1000: add initial
 XDP support

Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Tue, Sep 13, 2016 at 10:41:12PM +0000, Rustad, Mark D wrote:
>> That said, I can see that you have tried to keep the original code path
>> pretty much intact. I would note that you introduced rcu calls into the  
>> !bpf
>> path that would never have been done before. While that should be ok, I
>> would really like to see it tested, at least for the !bpf case, on real
>> hardware to be sure.
>
> please go ahead and test. rcu_read_lock is zero extra instructions
> for everything but preempt or debug kernels.

Well, I don't have any hardware in hand to test with, though my former  
employer would. I guess my current employer would too! :-) FWIW, the kernel  
used in that system I referred to before was a preempt kernel.

The test matrix is large, the tail is long and you can't just gloss these  
things over. I understand that it isn't the focus of your work, just as  
regression testing the e1000 is not the focus of any of our work any more.  
That is precisely why it is a sensitive area.

--
Mark Rustad, Networking Division, Intel Corporation

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