Re: [PATCH 2/6] net/hns3: fix inconsistent enabled RSS behavior

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 02 Mar 2022 15:46:37 +0100
Thomas Monjalon <thomas@monjalon.net> wrote:

> 02/03/2022 15:07, Ori Kam:
> > From: lihuisong (C) <lihuisong@huawei.com>  
> > > 在 2022/3/1 0:42, Ferruh Yigit 写道:  
> > > > On 2/28/2022 3:21 AM, Min Hu (Connor) wrote:  
> > > >> From: Huisong Li <lihuisong@huawei.com>
> > > >>
> > > >> RSS will not be enabled if the RTE_ETH_MQ_RX_RSS_FLAG isn't be set in
> > > >> dev_configure phase. However, if this flag isn't set, RSS can be enabled
> > > >> through the ethdev ops and rte_flow API. This behavior is contrary to
> > > >> each
> > > >> other.
> > > >>
> > > >> Fixes: c37ca66f2b27 ("net/hns3: support RSS")
> > > >> Cc: stable@dpdk.org
> > > >>
> > > >> Signed-off-by: Huisong Li <lihuisong@huawei.com>  
> > > >
> > > >
> > > > Hi Huisong, Connor,
> > > >
> > > > Let's get a little more feedback for this patch, cc'ed more people.
> > > >
> > > >
> > > > To enable RSS, multi queue mode should be set to
> > > > 'RTE_ETH_MQ_RX_RSS_FLAG'.
> > > >
> > > > But I wonder if it is required to configure RSS via flow API,  
> > > 
> > > I do not know the original purpose of adding the RSS configuration in
> > > flow API.
> > >   
> > The purpose is simple, this allow to create RSS per rule and not a global one.
> > For example create RSS that sends TCP to some queues while othe RSS will send
> > UDP traffic to different queues.
> >   
> > > However, as far as I know, the hash algorithm can be configured via this
> > > API,
> > > 
> > > but not via ethdev ops API.
> > >   
> > > > and if other PMDs check this configuration for flow API?  
> > > 
> > > Some PMDs already have similar check in RSS releated ops or rte_flow API.
> > > 
> > > For example, hinic, axbge, bnxt, cnxk, otx2, and ena.  
> 
> I suggest removing these checks.
> 
> > From my view point those are two different settings.
> > The RTE_ETH_MQ_RX_RSS_FLAG is global per port while
> > rte_flow is per rule.
> > 
> > I think, that if a PMD needs this flag, in order to enable it also for rte_flow then
> > it should be documented in the release note of the PMD.
> > It is a valid use case that the default traffic will not have RSS and only rules created by
> > rte_flow will have the RSS, for matching traffc.  
> 
> I think RTE_ETH_MQ_RX_RSS_FLAG should not be required by any PMD
> for rte_flow RSS rules.
> 
> 

Agreed.

The ideal state around RSS would be:
   - global settings affect the default started queues when device is started.
     if RSS is enabled and 4 queues are started, then RSS would happen for received
     packets across those 4 queues.
   - when adding new flow related rx:
      - new queues could be started - BUT not part of original RSS
      - new rte_flow rule can do RSS against the new flow:
            example:
              start queues 4,5,6,7
              rte_flow match TCP port 80 and process on queues 4,5,6,7 with RSS

This is a mess today, most devices work differently and there is no reference software
implementation.  In an ideal state, there would be a reference software implementation
that implements all of rte_flow, and all new hardware support would have to work the same
as the reference implementation. And there would be a full CI test suite around rte_flow.