Re: [dpdk-dev] Fwd: Disable receiving new flows on a core

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Nov 05, 2018 at 12:08:48AM +0000, Chintan Inbay wrote:
> 
> 
> 
> Begin forwarded message:
> 
> From: chintaninbay@outlook.com<mailto:chintaninbay@outlook.com>
> Date: November 1, 2018 at 6:19:49 PM PDT
> To: users@dpdk.org<mailto:users@dpdk.org>
> Subject: Disable receiving new flows on a core
> 
> Hi,
> 
> We use RSS for distributing flows across cores. Sometimes, in special cases we want to disable receiving new flows to a core. Only new flows. So say if RETA is programmed to receive on cores (0,1,2,3), then the new set would be (0,1,2).  Existing flows going to (3) should be retained and forwarded. Only new flows should not be sent to (3).
> 
> Eventually when core (3) is ready again, we need to re program RETA so that all four cores can take flows. So new set of cores would be (0,1,2,3)
> 
> Is this possible?

Not really, no. RSS does not track flows individually, only the hashes of
the flow's key fields. Therefore there is no way to separate old and new
flows, all you can do is move all flows that hash to value X to a new core.
Some of those may be old flows and some of them new. Note too that the size
of the RETA table limits the number of bits of that hash that are checked.
It's generally less than 10 bits.

/Bruce

> 
> Also if the process on core 3 goes down or crashes, is there a way to notify RSS hardware or you’d have to reprogram RETA in a signal handler?
> 
> Thanks,
> Chintan