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So for mergeable bufs, we use ewma machinery to guess the correct buffer size. If we don't guess correctly, XDP has to do aggressive copies. Problem is, xdp paths do not update the ewma at all, except sometimes with XDP_PASS. So whatever we happen to have before we attach XDP, will mostly stay around. The fix is probably to update ewma unconditionally. -- MST

So for mergeable bufs, we use ewma machinery to guess the correct buffer size. If we don't guess correctly, XDP has to do aggressive copies. Problem is, xdp paths do not update the ewma at all, except sometimes with XDP_PASS. So whatever we happen to have before we attach XDP, will mostly stay around. The fix is probably to update ewma unconditionally. -- MST

...t_hdr_mrg_rxbuf placed in top of buffer area). If that happens the XDP path does a xdp_linearize_page operation. The EWMA code is not used when headroom is defined, which e.g. gets enabled when running XDP. [1] https://lore.kernel.org/netdev/158824572816.2172139.1358700000273697123.stgit at firesoul/ -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer