Re: [PATCH vhost v3 00/19] virtio: drivers maintain dma info for premapped vq

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On Thu, 7 Mar 2024 13:28:27 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> On Wed, Mar 6, 2024 at 6:01 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> >
> > On Thu, 29 Feb 2024 04:34:20 -0500, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > > On Thu, Feb 29, 2024 at 05:02:37PM +0800, Xuan Zhuo wrote:
> > > > On Thu, 29 Feb 2024 03:21:14 -0500, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > > > > On Thu, Feb 29, 2024 at 03:20:25PM +0800, Xuan Zhuo wrote:
> > > > > > As discussed:
> > > > > > http://lore.kernel.org/all/CACGkMEvq0No8QGC46U4mGsMtuD44fD_cfLcPaVmJ3rHYqRZxYg@xxxxxxxxxxxxxx
> > > > > >
> > > > > > If the virtio is premapped mode, the driver should manage the dma info by self.
> > > > > > So the virtio core should not store the dma info.
> > > > > > So we can release the memory used to store the dma info.
> > > > > >
> > > > > > But if the desc_extra has not dma info, we face a new question,
> > > > > > it is hard to get the dma info of the desc with indirect flag.
> > > > > > For split mode, that is easy from desc, but for the packed mode,
> > > > > > it is hard to get the dma info from the desc. And for hardening
> > > > > > the dma unmap is saft, we should store the dma info of indirect
> > > > > > descs.
> > > > > >
> > > > > > So I introduce the "structure the indirect desc table" to
> > > > > > allocate space to store dma info with the desc table.
> > > > > >
> > > > > > On the other side, we mix the descs with indirect flag
> > > > > > with other descs together to share the unmap api. That
> > > > > > is complex. I found if we we distinguish the descs with
> > > > > > VRING_DESC_F_INDIRECT before unmap, thing will be clearer.
> > > > > >
> > > > > > Because of the dma array is allocated in the find_vqs(),
> > > > > > so I introduce a new parameter to find_vqs().
> > > > > >
> > > > > > Note:
> > > > > >     this is on the top of
> > > > > >         [PATCH vhost v1] virtio: packed: fix unmap leak for indirect desc table
> > > > > >         http://lore.kernel.org/all/20240223071833.26095-1-xuanzhuo@xxxxxxxxxxxxxxxxx
> > > > > >
> > > > > > Please review.
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > > v3:
> > > > > >     1. fix the conflict with the vp_modern_create_avq().
> > > > >
> > > > > Okay but are you going to address huge memory waste all this is causing for
> > > > > - people who never do zero copy
> > > > > - systems where dma unmap is a nop
> > > > >
> > > > > ?
> > > > >
> > > > > You should address all comments when you post a new version, not just
> > > > > what was expedient, or alternatively tag patch as RFC and explain
> > > > > in commit log that you plan to do it later.
> > > >
> > > >
> > > > Do you miss this one?
> > > > http://lore.kernel.org/all/1708997579.5613105-1-xuanzhuo@xxxxxxxxxxxxxxxxx
> > >
> > >
> > > I did. The answer is that no, you don't get to regress memory usage
> > > for lots of people then fix it up.
> > > So the patchset is big, I guess it will take a couple of cycles to
> > > merge gradually.
> >
> > Hi @Michael
> >
> > So, how about this patch set?
> >
> > I do not think they (dma maintainers) will agree the API dma_can_skip_unmap().
> >
> > If you think sq wastes too much memory using pre-mapped dma mode, how about
> > we only enable it when xsk is bond?
> >
> > Could you give me some advice?
>
> I think we have some discussion, one possible solution is:
>
> when pre mapping is enabled, virtio core won't store dma metadatas.
>
> Then it makes virtio-net align with other NIC.


YES.

This patch set works as this.

But the virtio-net must allocate too much memory to store dma and len.

num = queue size * 19

Michael thinks that waste too much memory.
	http://lore.kernel.org/all/20240225032330-mutt-send-email-mst@xxxxxxxxxx

So we try this:
	http://lore.kernel.org/all/20240301071918.64631-1-xuanzhuo@xxxxxxxxxxxxxxxxx

But I think that is difficult to be accepted by the  DMA maintainers.

So I have two advices:

1. virtio-net sq works without indirect.
	- that more like other NIC
	- the num of the memory to store the dma info is queue_size

2. The default mode of virtio-net sq is no-premapped
	- we just switch the mode when binding xsk

Thanks.


>
> Thanks
>
> >
> > Thanks.
> >
> >
> > >
> > > > I asked you. But I didnot recv your answer.
> > > >
> > > > Thanks.
> > > >
> > > >
> > > > >
> > > > > > v2:
> > > > > >     1. change the dma item of virtio-net, every item have MAX_SKB_FRAGS + 2
> > > > > >         addr + len pairs.
> > > > > >     2. introduce virtnet_sq_free_stats for __free_old_xmit
> > > > > >
> > > > > > v1:
> > > > > >     1. rename transport_vq_config to vq_transport_config
> > > > > >     2. virtio-net set dma meta number to (ring-size + 1)(MAX_SKB_FRGAS +2)
> > > > > >     3. introduce virtqueue_dma_map_sg_attrs
> > > > > >     4. separate vring_create_virtqueue to an independent commit
> > > > > >
> > > > > >
> > > > > >
> > > > > > Xuan Zhuo (19):
> > > > > >   virtio_ring: introduce vring_need_unmap_buffer
> > > > > >   virtio_ring: packed: remove double check of the unmap ops
> > > > > >   virtio_ring: packed: structure the indirect desc table
> > > > > >   virtio_ring: split: remove double check of the unmap ops
> > > > > >   virtio_ring: split: structure the indirect desc table
> > > > > >   virtio_ring: no store dma info when unmap is not needed
> > > > > >   virtio: find_vqs: pass struct instead of multi parameters
> > > > > >   virtio: vring_create_virtqueue: pass struct instead of multi
> > > > > >     parameters
> > > > > >   virtio: vring_new_virtqueue(): pass struct instead of multi parameters
> > > > > >   virtio_ring: simplify the parameters of the funcs related to
> > > > > >     vring_create/new_virtqueue()
> > > > > >   virtio: find_vqs: add new parameter premapped
> > > > > >   virtio_ring: export premapped to driver by struct virtqueue
> > > > > >   virtio_net: set premapped mode by find_vqs()
> > > > > >   virtio_ring: remove api of setting vq premapped
> > > > > >   virtio_ring: introduce dma map api for page
> > > > > >   virtio_ring: introduce virtqueue_dma_map_sg_attrs
> > > > > >   virtio_net: unify the code for recycling the xmit ptr
> > > > > >   virtio_net: rename free_old_xmit_skbs to free_old_xmit
> > > > > >   virtio_net: sq support premapped mode
> > > > > >
> > > > > >  arch/um/drivers/virtio_uml.c             |  31 +-
> > > > > >  drivers/net/virtio_net.c                 | 283 ++++++---
> > > > > >  drivers/platform/mellanox/mlxbf-tmfifo.c |  24 +-
> > > > > >  drivers/remoteproc/remoteproc_virtio.c   |  31 +-
> > > > > >  drivers/s390/virtio/virtio_ccw.c         |  33 +-
> > > > > >  drivers/virtio/virtio_mmio.c             |  30 +-
> > > > > >  drivers/virtio/virtio_pci_common.c       |  59 +-
> > > > > >  drivers/virtio/virtio_pci_common.h       |   9 +-
> > > > > >  drivers/virtio/virtio_pci_legacy.c       |  16 +-
> > > > > >  drivers/virtio/virtio_pci_modern.c       |  38 +-
> > > > > >  drivers/virtio/virtio_ring.c             | 698 ++++++++++++-----------
> > > > > >  drivers/virtio/virtio_vdpa.c             |  45 +-
> > > > > >  include/linux/virtio.h                   |  13 +-
> > > > > >  include/linux/virtio_config.h            |  48 +-
> > > > > >  include/linux/virtio_ring.h              |  82 +--
> > > > > >  tools/virtio/virtio_test.c               |   4 +-
> > > > > >  tools/virtio/vringh_test.c               |  28 +-
> > > > > >  17 files changed, 847 insertions(+), 625 deletions(-)
> > > > > >
> > > > > > --
> > > > > > 2.32.0.3.g01195cf9f
> > > > >
> > >
> >
>





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