Le 31/01/2016 16:24, Eric Dumazet a écrit : > On Sun, 2016-01-31 at 13:37 -0800, Tom Herbert wrote: >> Call get_unaligned_be32 when we access 32-bit fields in >> __skb_flow_dissect. At the beginning check for unlikely case of >> 1-byte aligned packet. >> >> Note that flow_dissector may be asked to parse packet unaligned >> fields in two instances: >> >> 1) Packet from a driver which is aligned to Ethernet header >> (2-byte alignment) >> 2) Parsing inner headers of a received GRE-TEB packet >> >> Testing: Ran super_netperf tests did not see a regression. This was on >> x86 which does not have problems with unaligned data. > > But this test is absolutely useless, what about testing arches that > actually care ? > > I am told all these MIPS based boxes have already not enough cpu power.
How about the Cavium OCTEON family and Broadcom/Netlogic XLR/XLP, those are massively multi-core and MIPS64 capable, even though they may not always run a Linux networking stack, some do. There are also plenty of ARMv7/ARMv8 devices out there that would benefit from proper alignment some might end-up using mlx4/5 and intel cards. > > It is sad, because none of them use the drivers that might call flow > dissection (mlx4 and 4 intel drivers) > > So I would rather fix the cases where flow dissection called from > eth_get_headlen() with non aligned stuff. > > And maybe restrict GRE-TEB to platforms with > CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y, since otherwise we need to add > these unaligned macros in thousands of places in our stacks. > > > -- Florian
