On 2018/07/24 12:38, Jakub Kicinski wrote: > On Tue, 24 Jul 2018 11:43:11 +0900, Toshiaki Makita wrote: >> On 2018/07/24 10:22, Jakub Kicinski wrote: >>> On Mon, 23 Jul 2018 00:13:06 +0900, Toshiaki Makita wrote: >>>> From: Toshiaki Makita <makita.toshi...@lab.ntt.co.jp> >>>> >>>> We need some mechanism to disable napi_direct on calling >>>> xdp_return_frame_rx_napi() from some context. >>>> When veth gets support of XDP_REDIRECT, it will redirects packets which >>>> are redirected from other devices. On redirection veth will reuse >>>> xdp_mem_info of the redirection source device to make return_frame work. >>>> But in this case .ndo_xdp_xmit() called from veth redirection uses >>>> xdp_mem_info which is not guarded by NAPI, because the .ndo_xdp_xmit is >>>> not called directly from the rxq which owns the xdp_mem_info. >>>> >>>> This approach introduces a flag in xdp_mem_info to indicate that >>>> napi_direct should be disabled even when _rx_napi variant is used. >>>> >>>> Signed-off-by: Toshiaki Makita <makita.toshi...@lab.ntt.co.jp> >>> >>> To be clear - you will modify flags of the original source device if it >>> ever redirected a frame to a software device like veth? Seems a bit >>> heavy handed. The xdp_return_frame_rx_napi() is only really used on >>> error paths, but still.. Also as you note the original NAPI can run >>> concurrently with your veth dest one, but also with NAPIs of other veth >>> devices, so the non-atomic xdp.rxq->mem.flags |= XDP_MEM_RF_NO_DIRECT; >>> makes me worried. >> >> xdp_mem_info is copied in xdp_frame in convert_to_xdp_frame() so the >> field is local to the frame. Changing flags affects only the frame. >> xdp.rxq is local to NAPI thread, so no worries about atomicity. > > Ah, right! mem_info used to be just 8B, now it would be 12B. > Alternatively we could perhaps add this info to struct redirect_info, > through xdp_do_redirect() to avoid the per-frame cost. I'm not sure > that's better.
OK, let me check if this works. -- Toshiaki Makita
