Hi Maciej, On Thu, Nov 17, 2022 at 01:03:04AM +0100, Maciej Fijalkowski wrote: > Hey Vladimir, > > have a look at xdp_convert_zc_to_xdp_frame() in net/core/xdp.c. For XDP_TX > on ZC Rx side we basically create new xdp_frame backed by new page and > copy the contents we had in ZC buffer. Then we give back the ZC buffer to > XSK buff pool and new xdp_frame has to be DMA mapped to HW. Ah, ok, I didn't notice the xdp_convert_zc_to_xdp_frame() call inside xdp_convert_buff_to_frame(), it's quite well hidden... So it's clear now from a correctness point of view, thanks for clarifying. This could spark a separate discussion about whether there is any better alternative to copying the RX buffer for XDP_TX and re-mapping to DMA something that was already mapped. But I'm not interested in that, since I believe who wrote the code probably thought about the high costs too. Anyway, I believe that in the general case (meaning from the perspective of the XSK API) it's perfectly fine to keep the RX buffer around for a while, nobody forces you to copy the frame out of it for XDP_TX.
