On Thu, Jun 18, 2020 at 11:12:57AM -0700, Eric Dumazet wrote: > > > On 6/18/20 9:09 AM, Jonathan Lemon wrote: > > Adds a "rx_hd_split" private flag parameter to ethtool. > > > > This enables header splitting, and sets up the fragment mappings. > > The feature is currently only enabled for netgpu channels. > > We are using a similar idea (pseudo header split) to implement 4096+(headers) > MTU at Google, > to enable TCP RX zerocopy on x86. > > Patch for mlx4 has not been sent upstream yet. > > For mlx4, we are using a single buffer of 128*(number_of_slots_per_RX_RING), > and 86 bytes for the first frag, so that the payload exactly fits a 4096 > bytes page. > > (In our case, most of our data TCP packets only have 12 bytes of TCP options) > > > I suggest that instead of a flag, you use a tunable, that can be set by > ethtool, > so that the exact number of bytes can be tuned, instead of hard coded in the > driver.
Sounds reasonable - in the long run, it would be ideal to have the hardware actually perform header splitting, but for now using a tunable fixed offset will work. In the same vein, there should be a similar setting for the TCP option padding on the sender side. -- Jonathan
