netdev - Re: [PATCH net-next] virtio_net: force_napi

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Message-ID: <CAF=yD-+Wvy_93h2=OV=hkrj7SRoR_NMpOyc8qMStUy74+6-t+Q@mail.gmail.com>
Date:   Wed, 1 Aug 2018 18:43:53 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     David Miller <davem@...emloft.net>, caleb.raitto@...il.com,
        Jason Wang <jasowang@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        Caleb Raitto <caraitto@...gle.com>
Subject: Re: [PATCH net-next] virtio_net: force_napi_tx module param.

 > > So e.g. we could set an affinity hint to a group of CPUs that
> > > might transmit to this queue.
> >
> > We also want to set the xps mask for all cpus in the group to this queue.
> >
> > Is there a benefit over explicitly choosing one cpu from the set, btw?
>
> If only one CPU actually transmits on this queue then probably yes.
> And virtio doesn't know whether that's the case.

Oh, yes, good example.

To plumb that through, vp_set_vq_affinity would have to take a cpu
mask like irq_set_affinity_hint, instead of a single value.

Though I don't suggest doing that as part of the core
virtnet_set_affinity changes.