Re: [dpdk-dev] [PATCH] examples/l3fwd: enable multiple Tx queues on a lcore

[Thomas Monjalon <thomas@monjalon.net>]

05/11/2020 10:24, Rong, Leyi:
> From: Jerin Jacob <jerinjacobk@gmail.com>
> > On Wed, Nov 4, 2020 at 2:34 PM Rong, Leyi <leyi.rong@intel.com> wrote:
> > > From: David Marchand <david.marchand@redhat.com>
> > > > On Wed, Nov 4, 2020 at 9:34 AM Rong, Leyi <leyi.rong@intel.com> wrote:
> > > > > As there always has thoughput limit for per queue, on some
> > > > > performance test case by using l3fwd, the result will limited by
> > > > > the per queue thoughput limit. With multiple Tx queue enabled, the
> > > > > per queue thoughput
> > > > > limit can be eliminated if the CPU core is not the bottleneck.
> > > >
> > > > Ah interesting.
> > > > Which nic has such limitations?
> > > > How much of an improvement can be expected from this?
> > >
> > > The initial found was on XXV710 25Gb NIC, but suppose such issue can
> > > happen on more NICs as the high-end CPU per core boundary is higher than
> > > many NICs(except 100Gb and above) per queue performance boundary.
> > > The improvement can be about 1.8X with that case@1t2q.
> > 
> > As far as I understand, the Current l3fwd Tx queue creation is like this:
> > If the app has N cores and M ports then l3fwd creates, N x M Tx queues in total,
> > What will be new values based on this patch?

Thank you Jerin for providing some info missing in the description of the patch.

> Hi Jacob,
> 
> Total queues number equals to queues per port multiply port number.
> Just take #l3fwd -l 5,6 -n 6 -- -p 0x3 --config '(0,0,5),(0,1,5),(1,0,6),(1,1,6)' as example, 
> With this patch appied, totally 2x2=4 tx queues can be polled, while only
> 1x2=2 tx queues can be used before.

It does not reply above question with N x M.

> > Does this patch has any regression in case the NIC queues able to cope up with
> > the throughput limit from CPU.
> 
> Regression test relevant with l3fwd passed with this patch, no obvious result drop 
> on other cases.

It does not reply the general question for all drivers you did not test.

As you probably noticed, this patch is blocked for months
because it is not properly explained.