Re: [dpdk-dev] [PATCH 3/4] examples/l3fwd: eliminate unnecessary reloads in loop

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Wednesday, April 14, 2021 1:43 AM
> To: Ruifeng Wang <Ruifeng.Wang@arm.com>
> Cc: jerinj@marvell.com; hemant.agrawal@nxp.com; Ferruh Yigit
> <ferruh.yigit@intel.com>; thomas@monjalon.net; David Marchand
> <david.marchand@redhat.com>; dpdk-dev <dev@dpdk.org>; nd
> <nd@arm.com>; Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Subject: Re: [dpdk-dev] [PATCH 3/4] examples/l3fwd: eliminate unnecessary
> reloads in loop
> 
> On Thu, Mar 18, 2021 at 3:56 PM Ruifeng Wang <ruifeng.wang@arm.com>
> wrote:
> >
> > Number of rx queue and number of rx port in lcore config are constants
> > during the period of l3 forward application running. But compiler has
> > no this information.
> >
> > Copied values from lcore config to local variables and used the local
> > variables for iteration. Compiler can see that the local variables are
> > not changed, so qconf reloads at each iteration can be eliminated.
> >
> > The change showed 1.8% performance uplift in single core, single port,
> > single queue test on N1SDP platform with MLX5 NIC.
> 
> At least, in octeontx2, I dont see any performance improvement.
> But change looks good. Please find below a comment.
> 
> >
> > Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > ---
> >  examples/l3fwd/l3fwd_lpm.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/examples/l3fwd/l3fwd_lpm.c b/examples/l3fwd/l3fwd_lpm.c
> > index 3dcf1fef1..d338590b9 100644
> > --- a/examples/l3fwd/l3fwd_lpm.c
> > +++ b/examples/l3fwd/l3fwd_lpm.c
> > @@ -190,14 +190,16 @@ lpm_main_loop(__rte_unused void *dummy)
> >         lcore_id = rte_lcore_id();
> >         qconf = &lcore_conf[lcore_id];
> >
> > -       if (qconf->n_rx_queue == 0) {
> > +       uint16_t n_rx_q = qconf->n_rx_queue;
> > +       uint16_t n_tx_p = qconf->n_tx_port;
> 
> How about adding const?

Ack. The values are not expected to be changed.
Will update in next version.