Actually, for the virtio drivers, we can enable premapped mode whatever
the value of use_dma_api. Because we provide the virtio dma apis.
So the driver can enable premapped mode unconditionally.
This patch set makes the big mode of virtio-net to support premapped mode.
And enable premapped mode for rx by default.
Based on the following points, we do not use page pool to manage these
pages:
1. virtio-net uses the DMA APIs wrapped by virtio core. Therefore,
we can only prevent the page pool from performing DMA operations, and
let the driver perform DMA operations on the allocated pages.
2. But when the page pool releases the page, we have no chance to
execute dma unmap.
3. A solution to #2 is to execute dma unmap every time before putting
the page back to the page pool. (This is actually a waste, we don't
execute unmap so frequently.)
4. But there is another problem, we still need to use page.dma_addr to
save the dma address. Using page.dma_addr while using page pool is
unsafe behavior.
5. And we need space the chain the pages submitted once to virtio core.
More:
https://lore.kernel.org/all/CACGkMEu=Aok9z2imB_c5qVuujSh=vjj1kx12fy9N7hqyi+M5Ow@xxxxxxxxxxxxxx/
Why we do not use the page space to store the dma?
http://lore.kernel.org/all/CACGkMEuyeJ9mMgYnnB42=hw6umNuo=agn7VBqBqYPd7GN=+39Q@xxxxxxxxxxxxxx
Please review.
v5: 1. Fix the comments from @Larysa Zaremba
http://lore.kernel.org/all/20240508063718.69806-1-xuanzhuo@xxxxxxxxxxxxxxxxx
v4:
1. For the conflict, switch to the net-next branch
v3:
1. big mode still use the mode that virtio core does the dma map/unmap
v2:
1. make gcc happy in page_chain_get_dma()
http://lore.kernel.org/all/202404221325.SX5ChRGP-lkp@xxxxxxxxx
v1:
1. discussed for using page pool
2. use dma sync to replace the unmap for the first page
Thanks.
Xuan Zhuo (4):
virtio_ring: enable premapped mode whatever use_dma_api
virtio_net: big mode skip the unmap check
virtio_net: rx remove premapped failover code
virtio_net: remove the misleading comment
drivers/net/virtio_net.c | 90 +++++++++++++++---------------------
drivers/virtio/virtio_ring.c | 7 +--
2 files changed, 38 insertions(+), 59 deletions(-)
--
2.32.0.3.g01195cf9f
