netdev - Re: [PATCH net-next v3 06/27] virtio_ring: introduce virtqueue_get_buf_ctx

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Message-ID: <CACGkMEvaTr1iT1M7DXN1PNOAZPM75BGv-wTOkyqb-7Sgjshwaw@mail.gmail.com>
Date: Thu, 11 Jan 2024 16:34:09 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v3 06/27] virtio_ring: introduce virtqueue_get_buf_ctx_dma()

On Fri, Dec 29, 2023 at 3:31 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> introduce virtqueue_get_buf_ctx_dma() to collect the dma info when
> get buf from virtio core for premapped mode.
>
> If the virtio queue is premapped mode, the virtio-net send buf may
> have many desc. Every desc dma address need to be unmap. So here we
> introduce a new helper to collect the dma address of the buffer from
> the virtio core.
>
> Because the BAD_RING is called (that may set vq->broken), so
> the relative "const" of vq is removed.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/virtio/virtio_ring.c | 174 +++++++++++++++++++++++++----------
>  include/linux/virtio.h       |  16 ++++
>  2 files changed, 142 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 51d8f3299c10..1374b3fd447c 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -362,6 +362,45 @@ static struct device *vring_dma_dev(const struct vring_virtqueue *vq)
>         return vq->dma_dev;
>  }
>
> +/*
> + *     use_dma_api premapped -> do_unmap
> + *  1. false       false        false
> + *  2. true        false        true
> + *  3. true        true         false
> + *
> + * Only #3, we should return the DMA info to the driver.

Btw, I guess you meant "#3 is false" here?

And could we reduce the size of these 3 * 3 matrices? It's usually a
hint that the code is not optmized.

Thanks