netdev - Re: [PATCH vhost 5/6] virtio_net: enable premapped by default

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Message-ID: <CACGkMEv2_wmXsh5uZhfZLQTtJX9633NdRL4KZrHumsTcr70-Sw@mail.gmail.com>
Date: Thu, 18 Apr 2024 14:26:33 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux.dev, "Michael S. Tsirkin" <mst@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH vhost 5/6] virtio_net: enable premapped by default

On Thu, Apr 11, 2024 at 10:51 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> Currently, big, merge, and small modes all support the premapped mode.
> We can now enable premapped mode by default. Furthermore,
> virtqueue_set_dma_premapped() must succeed when called immediately after
> find_vqs(). Consequently, we can assume that premapped mode is always
> enabled.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7ea7e9bcd5d7..f0faf7c0fe59 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -860,15 +860,13 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
>
>  static void virtnet_rq_set_premapped(struct virtnet_info *vi)
>  {
> -       int i;
> -
> -       /* disable for big mode */
> -       if (!vi->mergeable_rx_bufs && vi->big_packets)
> -               return;
> +       int i, err;
>
>         for (i = 0; i < vi->max_queue_pairs; i++) {
> -               if (virtqueue_set_dma_premapped(vi->rq[i].vq))
> -                       continue;
> +               err = virtqueue_set_dma_premapped(vi->rq[i].vq);
> +
> +               /* never happen */
> +               BUG_ON(err);

Nit:

Maybe just a BUG_ON(virtqueue_set_dma_premapped()).

Btw, if there's no way to disable pre mapping, maybe it's better to
rename virtqueue_set_dma_premapped() to
virtqueue_enable_dma_premapped(ing).

Thanks

>
>                 vi->rq[i].do_dma = true;
>         }
> --
> 2.32.0.3.g01195cf9f
>