netdev - Re: [PATCH v2 net-next 3/7] fou: Add GRO support

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Message-ID: <CA+mtBx_0F=Y-4FMGuuVeJKJqek7e7_TPmgDzR3FXvT-cuSO1bw@mail.gmail.com>
Date:	Mon, 15 Sep 2014 10:21:37 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Or Gerlitz <gerlitz.or@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 3/7] fou: Add GRO support

On Mon, Sep 15, 2014 at 10:03 AM, Or Gerlitz <gerlitz.or@...il.com> wrote:
> On Mon, Sep 15, 2014 at 6:10 PM, Tom Herbert <therbert@...gle.com> wrote:
>> On Mon, Sep 15, 2014 at 8:00 AM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>>> On Mon, Sep 15, 2014 at 6:07 AM, Tom Herbert <therbert@...gle.com> wrote:
>>>> Implement fou_gro_receive and fou_gro_complete, and populate these
>>>> in the correponsing udp_offloads for the socket. Added ipproto to
>>>> udp_offloads and pass this from UDP to the fou GRO routine in proto
>>>> field of napi_gro_cb structure.
>>>
>>>
>>> Do we really need that  extra hop of fou4_gro_receive/complete?
>>> can't we somehow plant the gro receive/complete (say) GRE handlers in
>>> the udp offload
>>> struct with the UDP port that related to (say) GRE over UDP tunneling?
>>>
>> That would be nice, but it isn't obvious to me how to manage the
>> references. The offload functions are accessed with RCU pretty consistently.
>
> Currently udp_gro_receive calls rcu_read_lock() before it invokes
> fou4/6_gro_receive
> and rcu_read_unlock after the fou calls returns. The Fou call repeats
> the same practice
> w.r.t the (say) GRE gro receive callback, so... what happens if we
> eliminate the fou part all together?

Yes, we could conceivably index into inet_offloads directly from
udp_gro_receive in lieu of calling the offload functions in the
structure. It is more special case code in udp though and I'm not sure
that makes it a win.
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