On 6/26/20 3:43 PM, Björn Töpel wrote:
From: Björn Töpel <bjorn.topel@xxxxxxxxx> When the AF_XDP buffer allocation API was introduced it had an optimization, "cheap_dma". The idea was that when the umem was DMA mapped, the pool also checked whether the mapping required a synchronization (CPU to device, and vice versa). If not, it would be marked as "cheap_dma" and the synchronization would be elided. In [1] Christoph points out that the optimization above breaks the DMA API abstraction, and should be removed. Further, Christoph points out that optimizations like this should be done within the DMA mapping core, and not elsewhere. Unfortunately this has implications for the packet rate performance. The AF_XDP rxdrop scenario shows a 9% decrease in packets per second. [1] https://lore.kernel.org/netdev/20200626074725.GA21790@xxxxxx/ Cc: Christoph Hellwig <hch@xxxxxx> Fixes: 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API") Signed-off-by: Björn Töpel <bjorn.topel@xxxxxxxxx>
Given there is roughly a ~5 weeks window at max where this removal could still be applied in the worst case, could we come up with a fix / proposal first that moves this into the DMA mapping core? If there is something that can be agreed upon by all parties, then we could avoid re-adding the 9% slowdown. :/ Thanks, Daniel
