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Tsirkin" , Jason Wang , Xuan Zhuo , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org Subject: [PATCH vhost v3 0/4] virtio_net: rx enable premapped mode by default Date: Wed, 24 Apr 2024 16:16:32 +0800 Message-Id: <20240424081636.124029-1-xuanzhuo@linux.alibaba.com> X-Mailer: git-send-email 2.32.0.3.g01195cf9f Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Git-Hash: 55c7001bc45b 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@mail.gmail.com/ Why we do not use the page space to store the dma? http://lore.kernel.org/all/CACGkMEuyeJ9mMgYnnB42=hw6umNuo=agn7VBqBqYPd7GN=+39Q@mail.gmail.com Please review. 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@intel.com 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