On Thu, 2015-07-30 at 09:58 -0700, Jörn Engel wrote:
> On Thu, Jul 30, 2015 at 05:22:55PM +0200, Mike Galbraith wrote:
> >
> > I piddled about with the thought that it might be nice to be able to
> > sprinkle cond_resched() about to cut rt latencies without wrecking
> > normal load throughput, cobbled together a cond_resched_rt().
> >
> > On my little box that was a waste of time, as the biggest hits are block
> > softirq and free_hot_cold_page_list().
>
> Block softirq is one of our problems as well. It is a bit of a joke
> that __do_softirq() moves work to ksoftirqd after 2ms, but block softirq
> can take several 100ms in bad cases.
>
> We could give individual softirqs a time budget. If they exceed the
> budget they should complete, but reassert themselves. Not sure about
> the rest, but that would be pretty simple to implement for block
> softirq.
Yeah, it wants something, not sure what though. Fix up every spot that
hinders rt performance, you'll end up with PREEMPT_RT, and generic
performance falls straight through the floor. Darn.
-Mike
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