Re: [PATCH bpf-next v2] libbpf: use implicit XSKMAP lookup from AF_XDP XDP program

On Mon, 21 Oct 2019 at 14:19, Toke Høiland-Jørgensen [off-list ref] wrote:

Björn Töpel [off-list ref] writes:

[...]

quoted

bpf_redirect_map() returns a 32-bit signed int, so the upper 32-bit
will need to be cleared. Having an explicit AND is one instruction
less than two shifts. So, it's an optimization (every instruction is
sacred).

OIC. Well, a comment explaining that might be nice (since you're doing
per-instruction comments anyway)? :)

Sure, I can do a v3 with a comment, unless someone has a better idea
avoiding both shifts and AND.

Thanks for taking a look!


Björn

-Toke