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    SubjectRe: [PATCH 3/3] Convert the UDP hash lock to RCU
    On Tue, Oct 07, 2008 at 09:16:13AM -0500, Christoph Lameter wrote:
    > Evgeniy Polyakov wrote:
    > > On Mon, Oct 06, 2008 at 06:08:09PM -0500, Corey Minyard (minyard@acm.org) wrote:
    > >> Would using SLAB_DESTROY_BY_RCU be ok, or would that be too expensive?
    > >
    > > I tested skb destruction via RCU path, and got 2.5 times worse numbers
    > > with small-packets-bulk-transfer workload.
    >
    > Was this with regular RCU freeing? This will cool down the cacheline before
    > frees. You need SLAB_DESTROY_BY_RCU to keep the objects cache hot.

    Indeed!

    But care is required -- SLAB_DESTROY_BY_RCU permits objects to be freed
    and reallocated while a reader holds a reference. The only guarantee is
    that the -type- of the data structure will not change while a reader holds
    a reference. With something like UDP, this might well be sufficient.

    Just be careful! ;-)

    Thanx, Paul


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