Hi, On 25/08/15 12:24, Bala Manoharan wrote:
The concern with adding additional has_hash_flag was that there will an "if check" in the system for every read hash value and since this comes in the fast path it might get costly if application reads it in several places. Anyhow that can be optimized by the implementation.
If the implementation can guarantee that it generates some hash for every packet, it can just return non-zero here, so the compiler can optimize it out. DPDK can be configured at pktio creation time to set up what kind of packets should be handled by RSS, therefore what headers are in the hash. But I guess we should expect that for non-supported protocols the hash value can end up undefined, so we should check the flag for sure. I think branch predictors can eliminate most of the performance impact.
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