netdev - Re: Performance regression on lan966x when extracting frames

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Date: Tue, 16 May 2023 10:04:32 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Horatiu Vultur <horatiu.vultur@...rochip.com>
Cc: netdev@...r.kernel.org
Subject: Re: Performance regression on lan966x when extracting frames

On Tue, May 16, 2023 at 9:45 AM Horatiu Vultur
<horatiu.vultur@...rochip.com> wrote:
>
> The 05/15/2023 14:30, Eric Dumazet wrote:
> >
> > On Mon, May 15, 2023 at 11:12 AM Horatiu Vultur
> > <horatiu.vultur@...rochip.com> wrote:
>
> Hi Eric,
>
> Thanks for looking at this.
>
> > >
> > > Hi,
> > >
> > > I have noticed that on the HEAD of net-next[0] there is a performance drop
> > > for lan966x when extracting frames towards the CPU. Lan966x has a Cortex
> > > A7 CPU. All the tests are done using iperf3 command like this:
> > > 'iperf3 -c 10.97.10.1 -R'
> > >
> > > So on net-next, I can see the following:
> > > [  5]   0.00-10.01  sec   473 MBytes   396 Mbits/sec  456 sender
> > > And it gets around ~97000 interrupts.
> > >
> > > While going back to the commit[1], I can see the following:
> > > [  5]   0.00-10.02  sec   632 MBytes   529 Mbits/sec   11 sender
> > > And it gets around ~1000 interrupts.
> > >
> > > I have done a little bit of searching and I have noticed that this
> > > commit [2] introduce the regression.
> > > I have tried to revert this commit on net-next and tried again, then I
> > > can see much better results but not exactly the same:
> > > [  5]   0.00-10.01  sec   616 MBytes   516 Mbits/sec    0 sender
> > > And it gets around ~700 interrupts.
> > >
> > > So my question is, was I supposed to change something in lan966x driver?
> > > or is there a bug in lan966x driver that pop up because of this change?
> > >
> > > Any advice will be great. Thanks!
> > >
> > > [0] befcc1fce564 ("sfc: fix use-after-free in efx_tc_flower_record_encap_match()")
> > > [1] d4671cb96fa3 ("Merge branch 'lan966x-tx-rx-improve'")
> > > [2] 8b43fd3d1d7d ("net: optimize ____napi_schedule() to avoid extra NET_RX_SOFTIRQ")
> > >
> > >
> >
> > Hmmm... thanks for the report.
> >
> > This seems related to softirq (k)scheduling.
> >
> > Have you tried to apply this recent commit ?
> >
> > Commit-ID:     d15121be7485655129101f3960ae6add40204463
> > Gitweb:        https://git.kernel.org/tip/d15121be7485655129101f3960ae6add40204463
> > Author:        Paolo Abeni <pabeni@...hat.com>
> > AuthorDate:    Mon, 08 May 2023 08:17:44 +02:00
> > Committer:     Thomas Gleixner <tglx@...utronix.de>
> > CommitterDate: Tue, 09 May 2023 21:50:27 +02:00
> >
> > Revert "softirq: Let ksoftirqd do its job"
>
> I have tried to apply this patch but the results are the same:
> [  5]   0.00-10.01  sec   478 MBytes   400 Mbits/sec  188 sender
> And it gets just a little bit bigger number of interrupts ~11000
>
> >
> >
> > Alternative would be to try this :
> >
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index b3c13e0419356b943e90b1f46dd7e035c6ec1a9c..f570a3ca00e7aa0e605178715f90bae17b86f071
> > 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -6713,8 +6713,8 @@ static __latent_entropy void
> > net_rx_action(struct softirq_action *h)
> >         list_splice(&list, &sd->poll_list);
> >         if (!list_empty(&sd->poll_list))
> >                 __raise_softirq_irqoff(NET_RX_SOFTIRQ);
> > -       else
> > -               sd->in_net_rx_action = false;
> > +
> > +       sd->in_net_rx_action = false;
> >
> >         net_rps_action_and_irq_enable(sd);
> >  end:;
>
> I have tried to use also this change with and without the previous patch
> but the result is the same:
> [  5]   0.00-10.01  sec   478 MBytes   401 Mbits/sec  256 sender
> And it is the same number of interrupts.
>
> Is something else that I should try?

High number of interrupts for a saturated receiver seems wrong.
(Unless it is not saturating the cpu ?)

Perhaps hard irqs are not properly disabled by this driver.

You also could try using napi_schedule_prep(), just in case it helps.

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
index bd72fbc2220f3010afd8b90f3704e261b9d0a98f..4694f4f34e6caf5cf540ada17a472c3c57f10823
100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
@@ -628,10 +628,12 @@ irqreturn_t lan966x_fdma_irq_handler(int irq, void *args)
        err = lan_rd(lan966x, FDMA_INTR_ERR);

        if (db) {
-               lan_wr(0, lan966x, FDMA_INTR_DB_ENA);
-               lan_wr(db, lan966x, FDMA_INTR_DB);
+               if (napi_schedule_prep(&lan966x->napi)) {
+                       lan_wr(0, lan966x, FDMA_INTR_DB_ENA);
+                       lan_wr(db, lan966x, FDMA_INTR_DB);

-               napi_schedule(&lan966x->napi);
+                       __napi_schedule(&lan966x->napi);
+               }
        }

        if (err) {