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    SubjectRe: irq load balancing
    On Thu, Sep 13, 2007 at 01:31:39PM -0700, Venkat Subbiah wrote:
    > Doing it in a round-robin fashion will be disastrous for performance.
    > Your cache miss rate will go through the roof and you'll hit the slow
    > paths in the network stack most of the time.
    > > Most of the work in my system is spent in enrypt/decrypting traffic.
    > Right now all this is done in a tasklet within the softirqd and hence
    > all landing up on the same CPU.
    > On the receive side it'a packet handler that handles the traffic. On the
    > tx side it's done within the transmit path of the packet. So would
    > re-architecting this to move the rx packet handler to a different kernel
    > thread(with smp affinity to one CPU) and tx to a different kernel
    > thread(with SMP affinity to a different CPU) be advisable.
    > What's the impact on cache miss and slowpath/fastpath in network stack.

    Since most network devices have a single status register for both
    receiver and transmit (and errors and the like), which needs a lock to
    protect access, you will likely end up with serious thrashing of moving
    the lock between cpus.

    Len Sorensen
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