On 15.04, Jesper Dangaard Brouer wrote: > > Out of curiosity, what is actually the performance impact on all > > of this? We were just arguing on a different matter on two more > > instructions in the fast-path, here it's refactoring the whole > > function into several ones, I presume gcc won't inline it. > > Pablo asked me to performance test this change. Full test report below. > > The performance effect (of this patch) depend on the Gcc compiler > version. > > Two tests: > 1. IP-forwarding (unloaded netfilter modules) > 2. Early drop in iptables "raw" table > > With GCC 4.4.7, which does not inline the new functions > (__netif_receive_skb_ingress and __netif_receive_skb_finish) the > performance impact/regression is definitly measurable. > > With GCC 4.4.7: > 1. IP-forwarding: +25.18 ns (slower) (-27776 pps) > 2. Early-drop : +7.55 ns (slower) (-66577 pps) > > With GCC 4.9.1, the new functions gets inlined, thus the refactor > splitup of __netif_receive_skb_core() is basically "cancled". > Strangly there is a small improvement for forwarding, likely due to > some lucky assember reordering that give less icache/fetch-misses. > The early-drop improvement is below accuracy levels, can cannot be > trusted. > > With GCC 4.9.1: > 1. IP-forwarding: -10.05ns (faster) (+17532 pps) > 2. Early-drop : -1.54ns (faster) (+16216 pps) below accuracy levels > > I don't know what to conclude, as the result depend on the compiler > version... but these kind of change do affect performance, and should > be tested/measured. Thanks Jesper. This effect without inlinging was to be expected I guess. The interesting question would be a patch that uses nf_hook() without okfn callback, moves the ingress qdisc to register with the netfilter ingress hook and moves the TTL tracking of ing_filter() to the ingress qdisc, where it belongs. My expectation would be that this would result in an overall performance gain. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
