netdev - Re: [PATCH net-next] virtio_net: ethtool tx napi configuration

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Message-ID: <CAF=yD-+hbtz3pXi5EYVsumqMEUE=E+Fq48+mKRj4Th8+jm8dMg@mail.gmail.com>
Date:   Thu, 27 Sep 2018 09:53:28 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>, caleb.raitto@...il.com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "Jon Olson (Google Drive)" <jonolson@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] virtio_net: ethtool tx napi configuration

On Thu, Sep 27, 2018 at 4:51 AM Jason Wang <jasowang@...hat.com> wrote:
>
>
>
> On 2018年09月14日 12:46, Willem de Bruijn wrote:
> >> I'm not sure I get this. If we don't enable tx napi, we tend to delay TX
> >> interrupt if we found the ring is about to full to avoid interrupt
> >> storm, so we're probably ok in this case.
> > I'm only concerned about the transition state when converting from
> > napi to no-napi when the queue is stopped and tx interrupt disabled.
> >
> > With napi mode the interrupt is only disabled if napi is scheduled,
> > in which case it will eventually reenable the interrupt. But when
> > switching to no-napi mode in this state no progress will be made.
> >
> > But it seems this cannot happen. When converting to no-napi
> > mode, set_coalesce waits for napi to complete in napi_disable.
> > So the interrupt should always start enabled when transitioning
> > into no-napi mode.
>
> An update, I meet a hang in napi_disalbe(). But it's hard to be
> reproduced. I tend to choose a easy way like V1 that only allow the
> switching when device is down.

I agree.

> I will post the patch after a vacation. (or you can post if it was
> urgent for you).

If you have time to review and add your signed-off-by, I can post it.
It's a pretty small diff at this point.

But no rush, we can also wait until after your vacation.

I also need to look at a patch to toggle LRO using ethtool, btw.