[ovs-discuss] If ovs doesn't masking process in flow_tbl_lookup, What are the disadvantages ?

Ben Pfaff blp at ovn.org
Fri Jun 9 04:29:42 UTC 2017


When OVS had only an in-kernel microflow cache, there were at least two
reasons for performance problems with many short-lived flows.  The first
was the cost of sending packets to userspace.  The second was the cost
of translating the packets through the entire OpenFlow pipeline.  The
megaflow cache solves both problems: it eliminates both the
kernel-to-user-to-kernel transition and (if the megaflow cache is
effective) the additional OpenFlow translations.

Regarding your second question, which flow rules are you asking about?

On Fri, Jun 09, 2017 at 12:22:09PM +0900, Heung Sik Choi wrote:
> What does "if only the microflow cache works" mean?
> 
> sorry to confuse you. I'm not good at English.
> 
> In the paper, the authors say that at start of ovs implementation, there
> has been microflow cache(EMC), but megaflow wasn't implemented.
> 
> At that time, they say  there was a problem caused by short lived
> connections.
> 
> I want to know the problem detail. I guess that the problem made ovs get
> flow rules from userlevel, and that made performance degradation.
> 
> also I want to know that when not using megaflow, are there big difference
> in aspect of number of flow rules.If there are the big difference, can you
> tell me the difference in numbers?
> 
> 
> 
> 2017-06-09 0:43 GMT+09:00 Ben Pfaff <blp at ovn.org>:
> 
> > On Thu, Jun 08, 2017 at 04:33:54PM +0900, Heung Sik Choi wrote:
> > > 1. If only microflow cache works and there are many short lived
> > > connections, does it make many tuples in table, and does it suffers
> > serious
> > > performance degradation by the many tuples(very many tuple makes context
> > > switching to Userlevel)?
> >
> > What does "if only the microflow cache works" mean?
> >
> > > 2. I know that OVS uses hash for table index. if only microflow cache and
> > > there are small amount of entries in the table, is it possible to find
> > > entry in O(1) time?
> >
> > Yes.
> >
> > > 3. In paper, microflow and megaflow use the word 'cache'. However, when I
> > > open the OVS code, it looks like they are in main memory area. doesn't
> > the
> > > 'cache' mean hardware cache?
> >
> > No.
> >


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