netdev - Re: Realtek 8139 problem on 486.

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Message-ID: <CAK8P3a0j+kSsEYwzdERJ7EZ8KheAPhyj+zYi645pbykrxgZYdQ@mail.gmail.com>
Date:   Wed, 9 Jun 2021 09:09:49 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Nikolai Zhubr <zhubr.2@...il.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: Realtek 8139 problem on 486.

On Wed, Jun 9, 2021 at 12:07 AM Nikolai Zhubr <zhubr.2@...il.com> wrote:
>
> 08.06.2021 23:45, Arnd Bergmann:
> > The idea was that all non-rx events that were pending at the start of the
> > function have been Acked at this point, by writing to the IntrMask
> > register before processing the particular event. If the same kind of event
> > arrives after the Ack, then opening in the mask should immediately trigger
> > the interrupt handler, which reactivates the poll function.
>
> Ok, it works, indeed. The overall bitrate seems lower somewhat.
> I'll re-test and benchmark some few variants (e.g. with and without busy
> loop) and report my findings.

If it's only a bit slower, that is not surprising, I'd expect it to
use fewer CPU
cycles though, as it avoids the expensive polling.

There are a couple of things you could do to make it faster without reducing
reliability, but I wouldn't recommend major surgery on this driver, I was just
going for the simplest change that would make it work right with broken
IRQ settings.

You could play around a little with the order in which you process events:
doing RX first would help free up buffer space in the card earlier, possibly
alternating between TX and RX one buffer at a time, or processing both
in a loop until the budget runs out would also help.

         Arnd