netdev - Re: [PATCH] virtio_net: send notification coalescing command only if value changed

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Date:   Wed, 21 Dec 2022 08:01:53 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alvaro Karsz <alvaro.karsz@...id-run.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH] virtio_net: send notification coalescing command only if
 value changed

On Wed, Dec 21, 2022 at 02:44:21PM +0200, Alvaro Karsz wrote:
> > Why do we bother? Resending needs more code and helps
> > reliability ...
> 
> It just seems unnecessary.
> If a user changes just one parameter:
> $ ethtool -C <iface> tx-usecs 30
> It will trigger 2 commands, including
> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET, even though no rx parameter changed.
> 
> If we'll add more ethtool coalescing parameters, changing one of the
> new parameter will trigger meaningless
> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET and VIRTIO_NET_CTRL_NOTF_COAL_TX_SET
> commands.
> 
> Alvaro

We'll always just do 2 commands, right?
I don't think we should bother at this point.
It might not be completely redundant.
E.g. if a card lost the config resending it might help fix things.


-- 
MST