[ovs-discuss] If ovs doesn't masking process in flow_tbl_lookup, What are the disadvantages ?
Heung Sik Choi
hschoi at os.korea.ac.kr
Fri Jun 9 04:47:14 UTC 2017
Thanks to reply.
Regarding your second question, which flow rules are you asking about?
I just want to know that when ovs had only an in-kernel microflow cache,
How many in-kernel cache miss there are, and also how much improving
there are when using megaflow.
And I have a last question. short-lived flows were main problem when there
was micro flow cache. I don't know the circumstance where short lived
connection happen often. can you let me know about it?
2017-06-09 13:29 GMT+09:00 Ben Pfaff <blp at ovn.org>:
> 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
> > in aspect of number of flow rules.If there are the big difference, can
> > 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
> > > > 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
> > > > 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.
> > > the
> > > > 'cache' mean hardware cache?
> > >
> > > No.
> > >
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