netdev - Re: [PATCH vhost 17/17] virtio_net: sq support premapped mode

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Message-ID: <CACGkMEtwWAijrLOrdgJ9ZPx5VjSfJtwVm1k1U8fsg9+tvgRHxg@mail.gmail.com>
Date: Thu, 1 Feb 2024 13:36:46 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux.dev, Richard Weinberger <richard@....at>, 
	Anton Ivanov <anton.ivanov@...bridgegreys.com>, Johannes Berg <johannes@...solutions.net>, 
	"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>, Hans de Goede <hdegoede@...hat.com>, 
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
	Vadim Pasternak <vadimp@...dia.com>, Bjorn Andersson <andersson@...nel.org>, 
	Mathieu Poirier <mathieu.poirier@...aro.org>, Cornelia Huck <cohuck@...hat.com>, 
	Halil Pasic <pasic@...ux.ibm.com>, Eric Farman <farman@...ux.ibm.com>, 
	Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, 
	Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Sven Schnelle <svens@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, 
	John Fastabend <john.fastabend@...il.com>, Benjamin Berg <benjamin.berg@...el.com>, 
	Yang Li <yang.lee@...ux.alibaba.com>, linux-um@...ts.infradead.org, 
	netdev@...r.kernel.org, platform-driver-x86@...r.kernel.org, 
	linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org, 
	kvm@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH vhost 17/17] virtio_net: sq support premapped mode

On Thu, Feb 1, 2024 at 11:28 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Wed, 31 Jan 2024 17:12:47 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > On Tue, Jan 30, 2024 at 7:43 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > >
> > > If the xsk is enabling, the xsk tx will share the send queue.
> > > But the xsk requires that the send queue use the premapped mode.
> > > So the send queue must support premapped mode.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > ---
> > >  drivers/net/virtio_net.c | 167 ++++++++++++++++++++++++++++++++++++++-
> > >  1 file changed, 163 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 226ab830870e..cf0c67380b07 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -46,6 +46,7 @@ module_param(napi_tx, bool, 0644);
> > >  #define VIRTIO_XDP_REDIR       BIT(1)
> > >
> > >  #define VIRTIO_XDP_FLAG        BIT(0)
> > > +#define VIRTIO_DMA_FLAG        BIT(1)
> > >
> > >  /* RX packet size EWMA. The average packet size is used to determine the packet
> > >   * buffer size when refilling RX rings. As the entire RX ring may be refilled
> > > @@ -140,6 +141,21 @@ struct virtnet_rq_dma {
> > >         u16 need_sync;
> > >  };
> > >
> > > +struct virtnet_sq_dma {
> > > +       union {
> > > +               struct virtnet_sq_dma *next;
> > > +               void *data;
> > > +       };
> > > +       dma_addr_t addr;
> > > +       u32 len;
> > > +       bool is_tail;
> > > +};
> > > +
> > > +struct virtnet_sq_dma_head {
> > > +       struct virtnet_sq_dma *free;
> > > +       struct virtnet_sq_dma *head;
> >
> > Any reason the head must be a pointer instead of a simple index?
>
>
> The head is used for kfree.
> Maybe I need to rename it.
>
> About the index(next) of the virtnet_sq_dma.
> If we use the index, the struct will be:
>
> struct virtnet_sq_dma {
>        dma_addr_t addr;
>        u32 len;
>
>        u32 next;
>        void *data
> };
>
> The size of virtnet_sq_dma is same.

Ok.

>
>
> >
> > > +};
> > > +
> > >  /* Internal representation of a send virtqueue */
> > >  struct send_queue {
> > >         /* Virtqueue associated with this send _queue */
> > > @@ -159,6 +175,8 @@ struct send_queue {
> > >
> > >         /* Record whether sq is in reset state. */
> > >         bool reset;
> > > +
> > > +       struct virtnet_sq_dma_head dmainfo;
> > >  };
> > >
>
> ....
>
> > > +
> > > +static int virtnet_sq_init_dma_mate(struct send_queue *sq)
> > > +{
> > > +       struct virtnet_sq_dma *d;
> > > +       int size, i;
> > > +
> > > +       size = virtqueue_get_vring_size(sq->vq);
> > > +
> > > +       size += MAX_SKB_FRAGS + 2;
> >
> > Is this enough for the case where an indirect descriptor is used?
>
>
> This is for the case, when the ring is full, the xmit_skb is called.
>
> I will add comment.

Just to make sure we are at the same page.

I meant, we could have more pending #sg than allocated here.

For example, we can have up to (vring_size - 2 - MAX_SKB_FRAGS) *
MAX_SKB_FRAGS number of pending sgs?

Thanks

>
> Thanks.
>
>
> >
> > Thanks
> >
>