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

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Date:   Thu, 27 Sep 2018 16:50:50 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.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 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 will post the patch after a vacation. (or you can post if it was 
urgent for you).

Thanks