Re: CONFIG_PREEMPT and server workloads

[Dipankar Sarma <dipankar@in.ibm.com>]

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