Message-ID: <20230516092714.wresm662w54zs226@soft-dev3-1>
Date: Tue, 16 May 2023 11:27:14 +0200
From: Horatiu Vultur <horatiu.vultur@...rochip.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: <netdev@...r.kernel.org>
Subject: Re: Performance regression on lan966x when extracting frames

The 05/16/2023 10:04, Eric Dumazet wrote:
> 
> 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 ?)

The CPU usage seems to be almost at 100%. This is the output of top
command:
149   132 root     R     5032   0%  96% iperf3 -c 10.97.10.1 -R
 12     2 root     SW       0   0%   3% [ksoftirqd/0]
150   132 root     R     2652   0%   1% top
...

> 
> 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);
> +               }
>         }

I get the same result as before with this.
[  5]   0.00-10.01  sec   477 MBytes   399 Mbits/sec  177 sender

I have applied this change without applying any of the other changes
that you suggested before. Should I apply also those the changes?

> 
>         if (err) {

-- 
/Horatiu

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