[ovs-dev] Clarification regarding Eviction mechanism on basis of Importance.

Shashwat Srivastava shashwat.srivastava at tcs.com
Thu Nov 27 04:04:06 UTC 2014


Hi Ben,

Thanks for the reply just wanted to confirm did you get any reply 
regarding the EXT-502 from ONF extensibility working group.

Also can you please let me know what will happen if the new flow enters 
the switch with same importance as the lowest importance in the flow 
table. Considering the earlier given example (new flow has importance=100 
and lowest flow in the existing flows has importance = 100), in this case 
will the existing flow will be evicted or the new flow will be dropped ?
Thanks in advance.



From:   Ben Pfaff <blp at nicira.com>
To:     Shashwat Srivastava <shashwat.srivastava at tcs.com>
Cc:     dev at openvswitch.com
Date:   10/30/2014 09:05 PM
Subject:        Re: Clarification regarding Eviction mechanism on basis of 
Importance.



On Thu, Oct 30, 2014 at 03:55:45PM +0530, Shashwat Srivastava wrote:
> I was going through openflow specs 1.4 and as mentioned in section 
> 7.3.4.1. page no. 73 "If the flag OFPTMPEF_IMPORTANCE is the only flag 
> set, eviction will
> be performed strictly in order of importance, that is flow entry with 
> lower importance will always be evicted before flow entry with higher 
> importance.", I have some queries regarding eviction behaviour.
> 
> Considering the case when Eviction is enabled on the basis of IMPORTANCE 

> (i.e. flows of lower importance will be evicted) and the table limit is 
> set to 5. Now suppose there are 5 flows of importance 
100,101,102,103,104.
> Now when the new flow is entered and has IMPORTANCE=10 and as the 
eviction 
> is enabled, the switch will evict flow having IMPORTANCE=100.
> Now is'nt this illogical to evict flow of higher importance (in this 
case 
> importance=100) for the new flow of lower importance (in this case 
> importance=10).
> 
> Considering the users above importance=50 as PLATINUM user and user with 

> importance < 50 as normal user. So for a normal user a platinum user's 
> service will be disrupted and will suffer loss of packet (although for 
> short period of time).

That is a good question.  I filed EXT-502, "Eviction when new flow is
less important than any existing flow," to pose this question for
clarification with the ONF extensibility working group.
 
> Kindly explain this behaviour of openvswitch ?

Open vSwitch doesn't have importance-based eviction, so there is nothing
in Open vSwitch to explain.

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