On 2014-01-14 14:50, Eric Dumazet wrote: > On Tue, 2014-01-14 at 14:22 -0500, Austin S Hemmelgarn wrote: > >> I disagree with the statement that current CPU's have reasonably fast >> dividers. A lot of embedded processors and many low-end x86 CPU's do >> not in-fact have any hardware divider, and usually provide it using >> microcode based emulation if they provide it at all. The AMD Jaguar >> micro-architecture in particular comes to mind, it uses an iterative >> division algorithm provided by the microcode that only produces 2 bits >> of quotient per cycle, even in the best case (2 8-bit integers and an >> integral 8-bit quotient) this still takes 4 cycles, which is twice as >> slow as any other math operation on the same processor. > > I doubt you run any BPF filter with a divide instruction in it on these > platform. > > Get real, do not over optimize things where it does not matter. > Actually, I have three Jaguar based routers, and use BPF regularly as part of their iptables rules to log certain packet types.
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