Re: [dpdk-dev] [PATCH v5] app/testpmd: fix the default RSS key configuration

[Ophir Munk <ophirmu@nvidia.com>]

> From: Ferruh Yigit <ferruh.yigit@intel.com>
> >>> On 10/15/2020 1:41 PM, Lijun Ou wrote:
> >>>> When start the testpmd, the pmd driver initializes the RSS
> >>>> configuration. Generally, the recommended RSS hash key is used as
> >>>> the default key in the driver. In addition, the default key is
> >>>> different from the default RSS flow in testpmd without specifying
> >>>> RSS hash key. So. if you do not specify the RSS key when creating
> >>>> an RSS rule, the testpmd uses the default key as the default RSS
> >>>> key of the RSS rule. As a result, you may mistakenly consider that
> >>>> the RSS key in use is the valid default key of the NIC, actually,
> >>>> the key and the valid default key of the NIC are two values.
> >>>>
> >>>> Consider the follow usage with testpmd:
> >>>> 1. first, startup testpmd:
> >>>> testpmd> show port 0 rss-hash key
> >>>> RSS functions:
> >>>>    all ipv4-frag ipv4-other ipv6-frag ipv6-other ip RSS key:
> >>>> -
> 6D5A56DA255B0EC24167253D43A38FB0D0CA2BCBAE7B30B477CB2DA3803
> 0F
> >>>> -20C6A42B73BBEAC01FA
> >>>> 2. create a rss rule
> >>>> testpmd> flow create 0 ingress pattern eth / ipv4 / udp / end
> >>>> testpmd> actions rss \
> >>>> types ipv4-udp end queues end / end
> >>>>
> >>>> 3. show rss-hash key
> >>>> testpmd> show port 0 rss-hash key
> >>>> RSS functions:
> >>>>    all ipv4-udp udp
> >>>> RSS key:
> >>>> -
> 74657374706D6427732064656661756C74205253532068617368206B65792C
> 206F
> >>>> -76657272696465
> >>>>
> >>>> In order to solve the above problems, it use the NIC valid default
> >>>> RSS key instead of the testpmd dummy RSS key in the flow
> >>>> configuration when the RSS key is not specified in the flow rule.
> >>>> If the NIC RSS key is invalid, it will use testpmd dummy RSS key as the
> default key.
> >>>>
> >>>> Fixes: ac8d22de2394 ("ethdev: flatten RSS configuration in flow
> >>>> API")
> >>>> Cc: stable@dpdk.org
> >>>>
> >>>> Signed-off-by: Lijun Ou <oulijun@huawei.com>
> >>>> Reviewed-by: Phil Yang <phil.yang@arm.com>
> >>>> ---
> >>>> V4->V5:
> >>>> -rewrite the commit log
> >>>> -add reviewed-by
> >>>
> >>> Hi Lijun,
> >>>
> >>> There were multiple other comments, it seems they are not addressed
> >>> but only updated the commit log, can you please check comments to
> prev versions.
> >>>
> >>> Before going into the details, my question was what happens if
> >>> default key not provided at all?
> >>> It seems this has been already tried by Ophir [1], later reverted
> >>> back [2] bringing the initial issue back.
> >>>
> >>> According commit, the reason of revert is to support following
> command:
> >>> "flow create 0 <pattern> actions rss queues 0 1 end key_len 40 / end"
> >>>
> >>> @Ophir, @Lijun,
> >>> Can we ignore the 'key_len' if the 'key' is not supported and solve
> >>> current issue as initially intended ([1])?
> >>>
> >> Hi, Ferruh
> >>    I have discussed with Phil Yang about the problem in [1]. I think
> >> there may be other problems with the idea and there is no better
> >> solution. and we need to remove key_len definition from rte_rss_conf
> >> structure. They don't have a plan. And [1] was eventually reverted.
> >>
> >
> > Why ignoring 'key_len' (set it to zero) when there is no 'key'
> > provided doesn't work?
> >
> 
> What do you think [1] + following update, will it work?
> 
>   diff --git a/lib/librte_ethdev/rte_flow.c b/lib/librte_ethdev/rte_flow.c
>   index ee4f3464fe..e7789c87b3 100644
>   --- a/lib/librte_ethdev/rte_flow.c
>   +++ b/lib/librte_ethdev/rte_flow.c
>   @@ -535,7 +535,7 @@ rte_flow_conv_action_conf(void *buf, const size_t
> size,
>                              }),
>                              size > sizeof(*dst.rss) ? sizeof(*dst.rss) : size);
>                   off = sizeof(*dst.rss);
>   -               if (src.rss->key_len) {
>   +               if (src.rss->key_len && src.rss->key) {
>                           off = RTE_ALIGN_CEIL(off, sizeof(*dst.rss->key));
>                           tmp = sizeof(*src.rss->key) * src.rss->key_len;
>                           if (size >= off + tmp)
> 

Ferruh, your suggestion ([1] + update) looks correct. I also verified it on mlx5 PMD.
Advantage: it's a generic fix for all dpdk applications using rte_flows (not just testpmd). 
It reduces code.
With this fix the responsibility of handling key==NULL and/or len==0 is moved to the PMDs (which is good).
 
With regard to Lijun patch - I liked the approach of overriding the default testpmd key with the default PMD key.
But it only addresses testpmd. More code was added. 
It seems OK to call rte_eth_dev_rss_hash_conf_get() as part of parsing RSS, but it would feel more confident if we could confirm it for all the PMDs (by testing) or at least review the PMDs rss_hash_conf_get() implementations.

> >> Thanks
> >> Lijun Ou
> >>>