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    SubjectRe: [RFC v1] hand off skb list to other cpu to submit to upper layer
    On Thu, 2009-03-05 at 09:04 +0800, Zhang, Yanmin wrote:
    > On Wed, 2009-03-04 at 01:39 -0800, David Miller wrote:
    > > From: "Zhang, Yanmin" <>
    > > Date: Wed, 04 Mar 2009 17:27:48 +0800
    > >
    > > > Both the new skb_record_rx_queue and current kernel have an
    > > > assumption on multi-queue. The assumption is it's best to send out
    > > > packets from the TX of the same number of queue like the one of RX
    > > > if the receved packets are related to the out packets. Or more
    > > > direct speaking is we need send packets on the same cpu on which we
    > > > receive them. The start point is that could reduce skb and data
    > > > cache miss.
    > >
    > > We have to use the same TX queue for all packets for the same
    > > connection flow (same src/dst IP address and ports) otherwise
    > > we introduce reordering.
    > > Herbert brought this up, now I have explicitly brought this up,
    > > and you cannot ignore this issue.
    > Thanks. Stephen Hemminger brought it up and explained what reorder
    > is. I answered in a reply (sorry for not clear) that mostly we need spread
    > packets among RX/TX in a 1:1 mapping or N:1 mapping. For example, all packets
    > received from RX 8 will be spreaded to TX 0 always.
    To make it clearer, I used 1:1 mapping binding when running testing
    on bensley (4*2 cores) and Nehalem (2*4*2 logical cpu). So there is no reorder
    issue. I also worked out a new patch on the failover path to just drop
    packets when qlen is bigger than netdev_max_backlog, so the failover path wouldn't
    cause reorder.

    > >
    > > You must not knowingly reorder packets, and using different TX
    > > queues for packets within the same flow does that.
    > Thanks for you rexplanation which is really consistent with Stephen's speaking.

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