linux-kernel - Re: virtio

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Date:   Mon, 17 May 2021 16:23:10 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Dave Taht <dave.taht@...il.com>
Cc:     Xianting Tian <xianting.tian@...ux.alibaba.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: virtio_net: BQL?

On Mon, May 17, 2021 at 2:44 PM Dave Taht <dave.taht@...il.com> wrote:
>
> Not really related to this patch, but is there some reason why virtio
> has no support for BQL?

There have been a few attempts to add it over the years.

Most recently, https://lore.kernel.org/lkml/20181205225323.12555-2-mst@redhat.com/

That thread has a long discussion. I think the key open issue remains

"The tricky part is the mode switching between napi and no napi."

> On Mon, May 17, 2021 at 11:41 AM Xianting Tian
> <xianting.tian@...ux.alibaba.com> wrote:
> >
> > BUG_ON() uses unlikely in if(), which can be optimized at compile time.
> >
> > Signed-off-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
> > ---
> >   drivers/net/virtio_net.c | 5 ++---
> >   1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index c921ebf3ae82..212d52204884 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1646,10 +1646,9 @@ static int xmit_skb(struct send_queue *sq, struct
> > sk_buff *skb)
> >         else
> >                 hdr = skb_vnet_hdr(skb);
> >
> > -       if (virtio_net_hdr_from_skb(skb, &hdr->hdr,
> > +       BUG_ON(virtio_net_hdr_from_skb(skb, &hdr->hdr,
> >                                     virtio_is_little_endian(vi->vdev), false,
> > -                                   0))
> > -               BUG();
> > +                                   0));
> >
> >         if (vi->mergeable_rx_bufs)
> >                 hdr->num_buffers = 0;
> > --
> > 2.17.1
> >
>
>
> --
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> Dave Täht CTO, TekLibre, LLC