Re: [dpdk-dev] [PATCH v5 1/5] i40e: Use constant random hash keys

["Zhang, Helin" <helin.zhang@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Monday, November 3, 2014 4:59 PM
> To: Zhang, Helin
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v5 1/5] i40e: Use constant random hash keys
> 
> 2014-11-03 08:18, Zhang, Helin:
> > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > The title is a bit surprising:
> > > - it should be about RSS
> >
> > RSS makes use of hash function to route received packets, though hash
> > function can be used for other cases, e.g. Flow director.
> 
> Yes but this patch is only changing rss_key_default so I guess it's only related to
> RSS, right?
Yes, it is currently for rss only.

> 
> > > - a constant cannot be really random ;)
The comments could be re-worded.

> >
> > The hash keys are generated by libc random function.
> > It is preparatory to avoid calling random function for each port.
> 
> Here, you remove the call to rte_rand by a constant value.
No need to calculate it every time, like what Linux i40e driver does.

> 
> > > 2014-10-21 11:14, Helin Zhang:
> > > > To be simpler, and remove the race condition, it uses prepared
> > > > constant random hash keys to replace runtime generating the hash keys.
> > >
> > > Could you explain what is the role of rss_key_default?
> >
> > Hash function needs to be configured with keys, before end users
> > configured them with specific keys, we need to provide a default keys
> > which is generated by libc random function.
> > The random keys can get the hash function to route the received
> > packets to all the queues well-proportioned.

Regards,
Helin