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

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Message-ID: <CAJs=3_CVUydOpH=a-RJLWUQ0_1EbkwKtGD2F3Xvw=dR5QFXP5g@mail.gmail.com>
Date:   Wed, 21 Dec 2022 14:44:21 +0200
From:   Alvaro Karsz <alvaro.karsz@...id-run.com>
To:     "Michael S. Tsirkin" <mst@...hat.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

> 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