Hi Adrien,
Tuesday, November 13, 2018 7:15 PM, Adrien Mazarguil:
> Subject: Re: [dpdk-dev] [PATCH v2] ethdev: document RSS default key and
> types
>
> Again a bit late to the party, please see below.
>
> On Sun, Nov 11, 2018 at 09:35:22AM +0000, Ori Kam wrote:
[...]
> > > The setfault is the result of commit a4391f8bae ("app/testpmd: set
> > > default RSS key as null").
> > > Reverting this commit should fix the segfault but it also means
> > > there is no way to set default key (key=NULL) with testpmd.
> > > Need to check if this is only a testpmd limitation and not all
> > > applications limitation.
> > >
> > > We should decide how an application can set default RSS without
> > > knowing anything about keys.
> > >
> >
> > I agree with Adrian that the main criteria should be the length.
> > Maybe the set default RSS in testpmd should get new parameter.
>
> Since [1] was reverted and we seem to agree that a zero key_len should
> trigger a PMD-specific default key, this can already be requested with
> testpmd by overriding key_len, e.g.:
>
> flow create 1 pattern eth / end actions rss key_len 0 / end
>
> Using an empty string as the key would yield the same result but cannot be
> expressed on the command line yet. Note that specifying a key automatically
> overrides key_len, so key_len must be forced to 0 last to get PMD defaults:
>
> flow create 1 pattern eth / end actions rss key foo key_len 0 / end
I don't understand why we are backing up API claims with "how testpmd is
implemented". The APIs should be correct, regardless of how testpmd is using
them.
To this doc issue,
I don't understand on what cases it makes sense for application to have
rss_key_len = 0 while rss_key != NULL. This is obviously in-consist input, and
of course all PMD will just ignore the key.
I think enforcing rss_key and rss_key_len to be NULL is a fair requirement from
application, and it makes no confusion in the API inputs.
>
> Here key_len is set to testpmd's default size when parsing "rss", updated to
> 3 when parsing "key foo" and updated once again when parsing "key_len 0".
>
> Lastly, while it would make sense for testpmd to use 0 as the default value,
> doing so yields inconsistent balancing results between vendors/devices as
> they all come with a different key. Same reason as initializing the RSS types
> field to the global rss_hf instead of 0.
>
> [1] "app/testpmd: revert setting default RSS"
>
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fma
> ils.dpdk.org%2Farchives%2Fdev%2F2018-
> November%2F118786.html&data=02%7C01%7Cshahafs%40mellanox.co
> m%7C0eecf3e9af4b4b6bc53108d6498ba2a8%7Ca652971c7d2e4d9ba6a4d1492
> 56f461b%7C0%7C0%7C636777261425388073&sdata=Hu0iGr2xS%2FI%2FI
> s5PtzCylMMft5w5TBmtd3GYppEKKcA%3D&reserved=0
>
> --
> Adrien Mazarguil
> 6WIND
