[ovs-dev] [PATCH 4/7] lib/flow: Add miniflow_extract_from_flow

[Ben Pfaff]

On Tue, Oct 07, 2014 at 02:51:59PM -0700, Jarno Rajahalme wrote:
> 
> On Oct 6, 2014, at 3:01 PM, Ben Pfaff <blp at nicira.com> wrote:
> 
> > On Wed, Oct 01, 2014 at 04:02:34PM -0700, Jarno Rajahalme wrote:
> >> miniflow_extract_from_flow() is faster than miniflow_init(), since it
> >> does not scan the fields not significant for the packet type. More
> >> importantly, it produces the same layout as miniflow_extract, which
> >> does not try to compress zero-valued packet header fields.
> >> 
> >> Signed-off-by: Jarno Rajahalme <jrajahalme at nicira.com>
> > 
> > I'm surprised that it's faster, since it's much more complex.
> > 
> > As for the layout, I can believe that it's the same (though it is
> > somewhat tricky to verify), but I wonder how to ensure that that
> > property is correctly maintained over time.  Do you have any thoughts?
> 
> I realized that Joe?s flow ID patches will make this patch mostly
> unnecessary, so I decided to drop this patch.
> 
> There is one remaining case where we need to convert a struct flow
> to struct netdev_flow_key. This is in dpif_netdev_flow_put(), which is
> no longer used for upcall processing (it is still used by probes). Since
> dpif_netdev_flow_put() is no longer performance critical, I decided to
> use flow_compose() and miniflow_extract() to first convert struct flow
> to a packet, and then extract it to a miniflow. This is trivially correct,
> so there is no issue with code maintenance in this regard.

I'm glad to hear all that.  Thanks.