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    SubjectRe: 8-CPU (SMP) #s for lockfree rtcache
    Hi Robert,

    On Tue, May 28, 2002 at 08:49:58AM -0700, Robert Love wrote:
    > > Well, the last time RCU was discussed, Linus said that he would
    > > like to see someplace where RCU clearly helps.
    > I agree the numbers posted are nice, but I remain skeptical like Linus.
    > Sure, the locking overhead is nearly gone in the profiled function where
    > RCU is used. But the overhead has just been _moved_ to wherever the RCU
    > work is now done. Any benchmark needs to include the damage done there,
    > too.

    Have you looked at the rt_rcu patch ? Where do you think there
    is overhead compared to what route cache alread does ? In my
    profiles, rcu routines and kernel mechanisms that it uses
    don't show high up. If you have any suggestions, then I can
    do an investigation.

    > I also balk at implicit locking...

    I agree that it is better to keep things simple and RCU isn't a
    replacement for locking. However the route cache hash table with
    refcount is a relatively simpler use of RCU and since it has
    benefits, we shouldn't shy away from using it if it is useful.

    Dipankar Sarma <>
    Linux Technology Center, IBM Software Lab, Bangalore, India.
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