From: Alexei Starovoitov Date: Fri, 25 May 2018 01:36:16 +0000 (-0700) Subject: Merge branch 'xdp_xmit-bulking' X-Git-Tag: v4.19~872^2~148^2 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=10f678683e4026e43524b0492068a371d00fdeed;p=platform%2Fkernel%2Flinux-rpi.git Merge branch 'xdp_xmit-bulking' Jesper Dangaard Brouer says: ==================== This patchset change ndo_xdp_xmit API to take a bulk of xdp frames. When kernel is compiled with CONFIG_RETPOLINE, every indirect function pointer (branch) call hurts performance. For XDP this have a huge negative performance impact. This patchset reduce the needed (indirect) calls to ndo_xdp_xmit, but also prepares for further optimizations. The DMA APIs use of indirect function pointer calls is the primary source the regression. It is left for a followup patchset, to use bulking calls towards the DMA API (via the scatter-gatter calls). The other advantage of this API change is that drivers can easier amortize the cost of any sync/locking scheme, over the bulk of packets. The assumption of the current API is that the driver implemementing the NDO will also allocate a dedicated XDP TX queue for every CPU in the system. Which is not always possible or practical to configure. E.g. ixgbe cannot load an XDP program on a machine with more than 96 CPUs, due to limited hardware TX queues. E.g. virtio_net is hard to configure as it requires manually increasing the queues. E.g. tun driver chooses to use a per XDP frame producer lock modulo smp_processor_id over avail queues. I'm considered adding 'flags' to ndo_xdp_xmit, but it's not part of this patchset. This will be a followup patchset, once we know if this will be needed (e.g. for non-map xdp_redirect flush-flag, and if AF_XDP chooses to use ndo_xdp_xmit for TX). --- V5: Fixed up issues spotted by Daniel and John V4: Splitout the patches from 4 to 8 patches. I cannot split the driver changes from the NDO change, but I've tried to isolated the NDO change together with the driver change as much as possible. ==================== Signed-off-by: Alexei Starovoitov --- 10f678683e4026e43524b0492068a371d00fdeed