Re: [dpdk-dev] [PATCH] fm10k: conditionally disable RSS during device initialization

[Michael Frasca <michael.frasca@oracle.com>]

Jing,

Thanks for your assistance. The experiment that you have built should allow you
to observe the bug. In [5], I would expect that queue 0 receives roughly 1/4 of
the packets that you sending, assuming the input packets have varied IP
addresses. Can you measure what % of packets are actually being received in this
single queue setup (after first running a 4-queue setup)?

When trying to running with only one RX queue, the fm10k retains the same RSS
hash function and redirection table that was configured from a previous run. As
a result, some packets are still being directed to other receive queues. I have
confirmed this by polling the queue specific stats, which I retrieved via
rte_eth_xstats_get().

Looking at fm10k_dev_rss_configure(), one should see that there is no
modification of fm10k registers when nb_rx_queues == 1. As far as I can tell,
this is the reason that only a certain partition of packets are being receive in
a single queue setup (after first running a multi-queue configuration).

I am unable to access my development environment today, but if you need, I can
later craft a patch to l3fwd that shows the measurement of packets received at
each queue.

Thanks,
Mike


> On Mar 24, 2016, at 2:40 AM, Chen, Jing D <jing.d.chen@intel.com> wrote:
> 
> Hi, Frasca,
> 
> 
> 
>> -----Original Message-----
>> From: Michael Frasca [mailto:michael.frasca@oracle.com <mailto:michael.frasca@oracle.com>]
>> Sent: Wednesday, March 23, 2016 9:43 PM
>> To: Chen, Jing D
>> Cc: dev@dpdk.org <mailto:dev@dpdk.org>
>> Subject: Re: [PATCH] fm10k: conditionally disable RSS during device
>> initialization
>> 
>> Hi Jing,
>> 
>> I ran into this issue while trying to run experiments with different RSS
>> configurations (no RSS being one cases). It is not clear to me that setting this
>> register to zero is the best way to disable RSS.
>> 
>> After digging further, I have a theory that I'm having this issues because I've
>> only attached my DPDK application to SR-IOV ports. In
>> fm10k_dev_dglort_map_configure(), I see that 'RSS Length' is set for the
>> DGLORT
>> decoder. However, it appears that this is only invoked for physical functions.
>> 
>> Could this be my problem? Is it required that I bind to the physical function
>> if I want to properly manipulate RSS?
>> 
>> Thanks,
>> Mike
>> 
> I don't know exactly what problem you ran into. I think we needn't worry about 
> those DGLORT setting when using VF device.
> 
> I've followed steps to use SRIOV device with RSS enabled and disabled, both
> are worked well from my side after applying your patch. Below is my setup.
> 
> 1. PF with Linux driver "fm10k-next_0.19.3".
> 2. DPDK with latest code from master branch, apply your patch.
> 3. Use 1 VF device created by kernel driver.
> 4. use l3fwd with " ./examples/l3fwd/build/l3fwd -c fc -n 4 -- -p 0x1 --config="(0,0,2),(0,1,2),(0,2,3),(0,3,3)""
>    with RSS enabled. After sending packets, I can see all 4 queues received packets.
> 5. use l3fwd with " ./examples/l3fwd/build/l3fwd -c fc -n 4 -- -p 0x1 --config="(0,0,2)""
>    with RSS disabled. After sending packets, I can see queue 0 received packets.
> 
> Can you explain what actual problem is?
> We can talk offline.