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    SubjectRe: UDP packets loss
    On Wed, 15 Nov 2006 00:15:47 +0200 (IST) wrote:

    > Hi,
    > I am running a client/server test app over IPOIB in which the client sends
    > a certain amount of data to the server. When the transmittion ends, the
    > server prints the bandwidth and how much data it received. I can see that
    > the server reports it received about 60% that the client sent. However,
    > when I look at the server's interface counters before and after the
    > transmittion, I see that it actually received all the data that the client
    > sent. This leads me to suspect that the networking layer somehow dropped
    > some of the data. One thing to not - the CPU is 100% busy at the receiver.
    > Could this be the reason (the machine I am using is 2 dual cores - 4
    > CPUs).

    If receiver application can't keep up UDP drops packets. The counter
    receive buffer errors (UDP_MIB_RCVBUFERRORS) is incremented.

    Don't expect flow control or reliable delivery; it's a datagram service!

    > The secod question is how do I make the interrupts be srviced by all CPUs?
    > I tried through the procfs as described by IRQ-affinity.txt but I can set
    > the mask to 0F bu then I read back and see it is indeed 0f but after a few
    > seconds I see it back to 02 (which means only CPU1).

    Most likely, the user level irq balance daemon (irqbalanced) is adjusting it?

    > One more thing - the device I am using is capable of generating MSIX
    > interrupts.

    Look at device capabilities with:

    lspci -vv

    Stephen Hemminger <>
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