netdev - Re: [PATCH v2 0/9] virtio: support advance DMA

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Date:   Wed, 30 Mar 2022 06:58:56 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "open list:XDP (eXpress Data Path)" <bpf@...r.kernel.org>
Subject: Re: [PATCH v2 0/9] virtio: support advance DMA

On Wed, Mar 30, 2022 at 06:51:53PM +0800, Xuan Zhuo wrote:
> On Wed, 30 Mar 2022 06:51:03 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> > On Wed, Mar 30, 2022 at 05:03:32PM +0800, Xuan Zhuo wrote:
> > > On Wed, 30 Mar 2022 16:38:18 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > > On Wed, Mar 30, 2022 at 2:59 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > > > >
> > > > > On Wed, 30 Mar 2022 14:56:17 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > > > > On Wed, Mar 30, 2022 at 2:34 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > > > > > >
> > > > > > > On Thu, Feb 24, 2022 at 07:03:53PM +0800, Xuan Zhuo wrote:
> > > > > > > > virtqueue_add() only supports virtual addresses, dma is completed in
> > > > > > > > virtqueue_add().
> > > > > > > >
> > > > > > > > In some scenarios (such as the AF_XDP scenario), DMA is completed in advance, so
> > > > > > > > it is necessary for us to support passing the DMA address to virtqueue_add().
> > > > > > >
> > > > > > > I picked up a couple of patches. Others are waiting for some acks
> > > > > > > (Jason?) and improved commit logs for documentation.
> > > > > >
> > > > > > I will review them.
> > > > >
> > > > > hi, the core code of premapped, I will merge it into 'virtio pci support
> > > > > VIRTIO_F_RING_RESET' because this function will be used when reusing the buffer
> > > > > after resize.
> > > >
> > > > I still prefer not to do that.
> > > >
> > > > We can make rest work for resize first and add pre mapping on top. It
> > > > will simplify the review.
> > >
> > > Yes, I am also worried about the review problem, the number of my local resize
> > > patch has reached 44 (including reuse bufs).
> > >
> > > hi, Michael, can we implement resize on top of v8 first? (drop unused bufs directly)
> > >
> > > Then we implement premmapd and reuse the bufs after resize.
> > >
> > > We need to get the address (DMA address) and len from the reset ring and submit
> > > it to the new vq through virtqueue_add(). So let virtqueue_add() support
> > > premapped first.
> > >
> > > Thanks.
> >
> > Not sure I understand.
> > So the plan is
> > - remap
> > - resize on top
> > ?
> 
> #1 resize with drop unused bufs directly
> #2 premapped and resize support reuse the unused bufs
> 
> This way "premaped" will have a user.
> 
> Between #1 and #2, I may submit some code with optimized formatting, because
> jason doesn't like my introduction of struct vring_split and struct vring_packed
> in #1 for passing parameters between extracted functions.
> 
> Thanks.

So let's start with 1. Direct drop for now is ok.


> 
> >
> >
> >
> > >
> > > >
> > > > Thanks
> > > >
> > > > >
> > > > > Thanks.
> > > > >
> > > > >
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > > >
> > > > > > > Thanks!
> > > > > > >
> > > > > > > > v2:
> > > > > > > >     1. rename predma -> premapped
> > > > > > > >     2. virtio net xdp tx use virtio dma api
> > > > > > > >
> > > > > > > > v1:
> > > > > > > >    1. All sgs requested at one time are required to be unified PREDMA, and several
> > > > > > > >       of them are not supported to be PREDMA
> > > > > > > >    2. virtio_dma_map() is removed from this patch set and will be submitted
> > > > > > > >       together with the next time AF_XDP supports virtio dma
> > > > > > > >    3. Added patch #2 #3 to remove the check for flags when performing unmap
> > > > > > > >       indirect desc
> > > > > > > >
> > > > > > > > Xuan Zhuo (9):
> > > > > > > >   virtio_ring: rename vring_unmap_state_packed() to
> > > > > > > >     vring_unmap_extra_packed()
> > > > > > > >   virtio_ring: remove flags check for unmap split indirect desc
> > > > > > > >   virtio_ring: remove flags check for unmap packed indirect desc
> > > > > > > >   virtio_ring: virtqueue_add() support premapped
> > > > > > > >   virtio_ring: split: virtqueue_add_split() support premapped
> > > > > > > >   virtio_ring: packed: virtqueue_add_packed() support premapped
> > > > > > > >   virtio_ring: add api virtio_dma_map() for advance dma
> > > > > > > >   virtio_ring: introduce virtqueue_add_outbuf_premapped()
> > > > > > > >   virtio_net: xdp xmit use virtio dma api
> > > > > > > >
> > > > > > > >  drivers/net/virtio_net.c     |  42 +++++-
> > > > > > > >  drivers/virtio/virtio_ring.c | 280 ++++++++++++++++++++++++++---------
> > > > > > > >  include/linux/virtio.h       |  12 ++
> > > > > > > >  3 files changed, 254 insertions(+), 80 deletions(-)
> > > > > > > >
> > > > > > > > --
> > > > > > > > 2.31.0
> > > > > > >
> > > > > >
> > > > >
> > > >
> >