[ovs-dev] faq: Expand on answer about packet buffering removal.

Submitted by Ben Pfaff on March 17, 2017, 3:16 p.m.

Details

Message ID 20170317151606.31912-1-blp@ovn.org
State Superseded
Headers show

Commit Message

Ben Pfaff March 17, 2017, 3:16 p.m.
Signed-off-by: Ben Pfaff <blp@ovn.org>
---
 Documentation/faq/openflow.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

andy zhou March 29, 2017, 5:25 p.m.
On Fri, Mar 17, 2017 at 8:16 AM, Ben Pfaff <blp@ovn.org> wrote:
> Signed-off-by: Ben Pfaff <blp@ovn.org>
> ---
>  Documentation/faq/openflow.rst | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/Documentation/faq/openflow.rst b/Documentation/faq/openflow.rst
> index 376e64eb4482..214e38e6a9aa 100644
> --- a/Documentation/faq/openflow.rst
> +++ b/Documentation/faq/openflow.rst
> @@ -462,6 +462,14 @@ What's going on?
>      messages and will send an error response if any other value of this field
>      is included in a "packet-out" or a "flow mod" sent by a controller.
>
> +    Packet buffers have limited usefulness in any case.  Table-miss packet-in
> +    messages most commonly pass the first packet in a microflow to the OpenFlow
> +    controller, which then sets up an OpenFlow flow that handles remaining
> +    traffic in the microflow without further controller intervention.  In such
> +    a case, the packet that initiates the microflow is usually small, which
> +    means that the switch sends the entire packet to the controller and the
> +    buffer only saves a small number of bytes in the reverse direction.
> +
I can see that In case of TCP, the packet buffer is usually small
(except DOS). But
it is not clear to me that why this is true in general. May be you
mean this is what we
have observed in practice?

Patch hide | download patch | download mbox

diff --git a/Documentation/faq/openflow.rst b/Documentation/faq/openflow.rst
index 376e64eb4482..214e38e6a9aa 100644
--- a/Documentation/faq/openflow.rst
+++ b/Documentation/faq/openflow.rst
@@ -462,6 +462,14 @@  What's going on?
     messages and will send an error response if any other value of this field
     is included in a "packet-out" or a "flow mod" sent by a controller.
 
+    Packet buffers have limited usefulness in any case.  Table-miss packet-in
+    messages most commonly pass the first packet in a microflow to the OpenFlow
+    controller, which then sets up an OpenFlow flow that handles remaining
+    traffic in the microflow without further controller intervention.  In such
+    a case, the packet that initiates the microflow is usually small, which
+    means that the switch sends the entire packet to the controller and the
+    buffer only saves a small number of bytes in the reverse direction.
+
 Q: How does OVS divide flows among buckets in an OpenFlow "select" group?
 
     A: In Open vSwitch 2.3 and earlier, Open vSwitch used the destination