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    SubjectRe: CONFIG_PREEMPT and server workloads
    On Sat, Mar 20, 2004 at 01:24:11PM +0100, Andrea Arcangeli wrote:
    > On Fri, Mar 19, 2004 at 10:52:03PM +0530, Dipankar Sarma wrote:
    > > the overall problem, IMO. I am collecting some instrumentation
    > > data to understand softirq/rcu behavior during heavy loads and
    > > ways to counter long running softirqs.
    > >
    > > Latency isn't the only issue. DoS on route cache is another
    > > issue that needs to be addressed. I have been experimenting
    > > with Robert Olsson's router test and should have some more results
    > > out soon.
    >
    > why don't you simply interrupt rcu_do_batch after a dozen of callbacks?
    > if it gets interrupted you then go ahead and you splice the remaining
    > entries into another list for a tasklet, then the tasklet will be a
    > reentrant one, so the ksoftirqd will take care of the latency.
    >
    > the only valid reason to use the timer irq instead of the tasklet in the
    > first place is to delay the rcu invocation and coalesce the work
    > together, but if there's too much work to do you must go back to the
    > tasklet way that has always been scheduler-friendy.

    Andrea, I *am* working on a throttling mechanism for rcu/softirqs.
    I just didn't see the point in publishing it until I had the
    measurement results in hand :)

    I will publish the results under both router DoS and filesystem workload.

    Thanks
    Dipankar
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