On Sun, 30 Jun 2019 20:23:48 +0300 Ivan Khoronzhuk <ivan.khoronz...@linaro.org> wrote:
> Add XDP support based on rx page_pool allocator, one frame per page. > Page pool allocator is used with assumption that only one rx_handler > is running simultaneously. DMA map/unmap is reused from page pool > despite there is no need to map whole page. > > Due to specific of cpsw, the same TX/RX handler can be used by 2 > network devices, so special fields in buffer are added to identify > an interface the frame is destined to. Thus XDP works for both > interfaces, that allows to test xdp redirect between two interfaces > easily. Aslo, each rx queue have own page pools, but common for both > netdevs. Looking at the details what happen when a single RX-queue can receive into multiple net_device'es. I realize that this driver will violate/kill some of the "hidden"/implicit RX-bulking that the XDP_REDIRECT code depend on for performance. Specifically, it violate this assumption: https://github.com/torvalds/linux/blob/v5.2-rc7/kernel/bpf/devmap.c#L324-L329 /* Ingress dev_rx will be the same for all xdp_frame's in * bulk_queue, because bq stored per-CPU and must be flushed * from net_device drivers NAPI func end. */ if (!bq->dev_rx) bq->dev_rx = dev_rx; This drivers "NAPI func end", can have received into multiple net_devices, before it's NAPI cycle ends. Thus, violating this code assumption. Knowing all xdp_frame's in the bulk queue is from the same net_device, can be used to further optimize XDP. E.g. the dev->netdev_ops->ndo_xdp_xmit() call don't take fully advantage of this, yet. If we merge this driver, it will block optimizations in this area. NACK -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
