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Date: Wed, 21 Apr 2010 11:39:33 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: Franco Fichtner <franco@...tsummer.de> Cc: Tom Herbert <therbert@...gle.com>, Changli Gao <xiaosuo@...il.com>, David Miller <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [PATCH net-next-2.6] rps: consistent rxhash Le mercredi 21 avril 2010 à 11:29 +0200, Franco Fichtner a écrit : > Tom Herbert wrote: > >> I thought about this for some time... > >> > >> Do we really need the port numbers here at all? A simple > >> addr1^addr2 can provide a good enough pointer for > >> distribution amongst CPUs. > >> > > > > What about a server behind a TCP proxy? Also, need to minimize > > collisions for RPS to be effective > > What about routers? What about loopback? This all boils down to > the same issue of obscuring IP data by "magical" means and then > reattaching functionality by reaching for upper layer information. > It is necessary in some cases, but it can cripple performance > for other cases. > > The interesting thing is you don't need to deal with collisions > while distributing amonst cpus at all. You just need to make sure > the distribution algorithm keeps every single flow attached to > the correct cpu. > > All of the actual flow hashing, tracking and whatever else the > traffic needs to go through can be done locally by cpu x which > helps a lot with load distribution and cache issues in mind. It > also helps locking because there is no global flow lookup table. > Oh, and it also reduces collisions with every cpu you add for > receiving. > > I work with a lot of plain office and ISP traffic in mind daily, > so please don't misunderstand my motivation here. I'd hate to > see poor performance in scenarios in which there is a lot of > potential improvement. > I am a bit lost by this conversation. Are you saying something is wrong with current schem ? What are exactly your suggestions ? Tom replied to you that a hash derived from (addr1 ^ addr2) would not work in situations where all flows goes from machine A to machine B (all hashes would be the same) Current hash is probably more than enough to cover all situations. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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