Re: [dpdk-dev] i40e and RSS woes

[Gleb Natapov <gleb@cloudius-systems.com>]

On Thu, Mar 05, 2015 at 05:56:27AM +0000, Zhang, Helin wrote:
> Hi Gleb
> 
> Sorry for late! I am struggling on my tasks for the following DPDK release these days.
> 
> > -----Original Message-----
> > From: Gleb Natapov [mailto:gleb@cloudius-systems.com]
> > Sent: Monday, March 2, 2015 8:56 PM
> > To: dev@dpdk.org
> > Cc: Zhang, Helin
> > Subject: Re: i40e and RSS woes
> > 
> > Ping.
> > 
> > On Thu, Feb 19, 2015 at 04:50:10PM +0200, Gleb Natapov wrote:
> > > CCing i40e driver author in a hope to get an answer.
> > >
> > > On Mon, Feb 16, 2015 at 03:36:54PM +0200, Gleb Natapov wrote:
> > > > I have an application that works reasonably well with ixgbe driver,
> > > > but when I try to use it with i40e I encounter various RSS related issues.
> > > >
> > > > First one is that for some reason i40e, when it builds default reta
> > > > table, round down number of queues to power of two. Why is this? If
> It seems because of i40e queue configuration. We will check it more and see
> if it can be changed or improved later.
> 
Thanks, as I said below when I configure reta by myself everything work
as expected - traffic is received on all queues, so I am curious if in some
scenarios my code can break.

> > > > I configure reta by my own using all of the queues everything seams
> > > > to be working. To add insult to injury I do not get any errors
> > > > during configuration some queues just do not receive any traffic.
> > > >
> > > > The second problem is that for some reason i40e does not use 40 byte
> > > > toeplitz hash key like any other driver, but it expects the key to
> > > > be 52 bytes. And it would have being fine (if we ignore the fact
> > > > that it contradicts MS spec), but how my high level code suppose to know
> > that?
> Actually a rss_key_len was introduced in struct rte_eth_rss_conf recently. So the
> length should be indicated clearly. But I found the annotations of that structure
> should have been reworked. I will try to rework it with clear descriptions.
> 
I saw rss_key_len of course, my question is how my code suppose to know
what value to set it to? Why required key length is not part of a device
capability query (or is it and I missed it)? The only way I found to get
key length is to quire device for a key, and check rss_key_len. If it
is zero then key is 40 bytes, otherwise whatever rss_key_len says. This
method is more of a hack then proper way to do it.

> > > > And again, device configuration does not fail when wrong key length
> > > > is provided, it just uses some other key. Guys this kind of error
> > > > handling is completely unacceptable.
> If less length of key is provided, it will not be used at all, the default key will be used.
> So there is no issue as you said. But we need to add more clear description for the
> structure of rte_eth_rss_conf.
> 
What you've said above is exactly the issue! My code does not work if
a key used by HW is not the same as was set by application, but since
I get no error when my setting is ignored the is not way for me to know
that my application will not work (short of querying key back and comparing
which is again a hack). Device configuration should fail if it cannot
apply my settings.

--
			Gleb.