Re: Performance regression on lan966x when extracting frames

[Horatiu Vultur <horatiu.vultur@microchip.com>]

The 05/15/2023 14:30, Eric Dumazet wrote:
> 
> On Mon, May 15, 2023 at 11:12 AM Horatiu Vultur
> <horatiu.vultur@microchip.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@redhat.com>
> AuthorDate:    Mon, 08 May 2023 08:17:44 +02:00
> Committer:     Thomas Gleixner <tglx@linutronix.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?

-- 
/Horatiu