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

Jason Wang
2024-03-08T06:03:55Z

On Thu, Mar 7, 2024 at 4:15 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Thu, 7 Mar 2024 13:28:27 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > On Wed, Mar 6, 2024 at 6:01 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > On Thu, 29 Feb 2024 04:34:20 -0500, "Michael S. Tsirkin" <mst@redhat.com> 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@redhat.com> wrote:
> > > > > > On Thu, Feb 29, 2024 at 03:20:25PM +0800, Xuan Zhuo wrote:
> > > > > > > As discussed:
> > > > > > > http://lore.kernel.org/all/CACGkMEvq0No8QGC46U4mGsMtuD44fD_cfLcPaVmJ3rHYqRZxYg@mail.gmail.com
> > > > > > >
> > > > > > > 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@linux.alibaba.com
> > > > > > >
> > > > > > > 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@linux.alibaba.com
> > > >
> > > >
> > > > 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@kernel.org
>
> So we try this:
> http://lore.kernel.org/all/20240301071918.64631-1-xuanzhuo@linux.alibaba.com
>
> 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

This requires benchmarks.

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

This could be one step.

We can hear from Michael.

Thanks

>
> 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
> > > > > >
> > > >
> > >
> >
>