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

["Rong, Leyi" <leyi.rong@intel.com>]

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Thursday, November 5, 2020 3:15 PM
> To: Rong, Leyi <leyi.rong@intel.com>
> Cc: David Marchand <david.marchand@redhat.com>; Zhang, Qi Z
> <qi.z.zhang@intel.com>; dev <dev@dpdk.org>
> Subject: Re: [dpdk-dev] [PATCH] examples/l3fwd: enable multiple Tx queues on
> a lcore
> 
> On Wed, Nov 4, 2020 at 2:34 PM Rong, Leyi <leyi.rong@intel.com> wrote:
> >
> >
> > > -----Original Message-----
> > > From: David Marchand <david.marchand@redhat.com>
> > > Sent: Wednesday, November 4, 2020 4:43 PM
> > > To: Rong, Leyi <leyi.rong@intel.com>
> > > Cc: Zhang, Qi Z <qi.z.zhang@intel.com>; dev <dev@dpdk.org>
> > > Subject: Re: [PATCH] examples/l3fwd: enable multiple Tx queues on a
> > > lcore
> > >
> > > On Wed, Nov 4, 2020 at 9:34 AM Rong, Leyi <leyi.rong@intel.com> wrote:
> > > > > -----Original Message-----
> > > > > From: David Marchand <david.marchand@redhat.com>
> > > > > Sent: Wednesday, November 4, 2020 4:14 PM
> > > > > To: Rong, Leyi <leyi.rong@intel.com>
> > > > > Cc: Zhang, Qi Z <qi.z.zhang@intel.com>; dev <dev@dpdk.org>
> > > > > Subject: Re: [PATCH] examples/l3fwd: enable multiple Tx queues
> > > > > on a lcore
> > > > >
> > > > > If I count well, this is the v3 of the patch.
> > > > > Please version your patches.
> > > >
> > > > The previous versions are set to superseded. As nothing changes
> > > > with content on those versions, can start from this version?
> > >
> > > The commitlog changes even if the code itself did not change, so
> > > this is a different patch.
> > > Different patches mean different versions.
> > > This shows that some work happened since the v1 submission.
> > >
> >
> > Agreed.
> > >
> > > > 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?
> > >
> > >
> > > --
> > > David Marchand
> >
> > 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?
> 

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.


> 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.

> 
> >
> > Leyi
> >