Messages in this thread | | | Date | Thu, 18 Oct 2018 12:33:32 +0200 | From | luca abeni <> | Subject | Re: INFO: rcu detected stall in do_idle |
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Hi Peter,
On Thu, 18 Oct 2018 11:48:50 +0200 Peter Zijlstra <peterz@infradead.org> wrote: [...] > > So, I tend to think that we might want to play safe and put some > > higher minimum value for dl_runtime (it's currently at 1ULL << > > DL_SCALE). Guess the problem is to pick a reasonable value, though. > > Maybe link it someway to HZ? Then we might add a sysctl (or > > similar) thing with which knowledgeable users can do whatever they > > think their platform/config can support? > > Yes, a HZ related limit sounds like something we'd want. But if we're > going to do a minimum sysctl, we should also consider adding a > maximum, if you set a massive period/deadline, you can, even with a > relatively low u, incur significant delays.
I agree with this.
> And do we want to put the limit on runtime or on period ?
I think we should have a minimum allowed runtime, a maximum allowed runtime, a minimum allowed period and a (per-user? per-control group?) maximum allowed utilization.
I suspect having a maximum period is useless, if we already enforce a maximum runtime.
> That is, something like: > > TICK_NSEC/2 < period < 10*TICK_NSEC
As written above I would not enforce a maximum period.
> > and/or > > TICK_NSEC/2 < runtime < 10*TICK_NSEC
I think (but I might be wrong) that "TICK_NSEC/2" is too large... I would divide the tick for a larger number (how many time do we want to allow the loop to run?)
And I think the maximum runtime should not be TICK-dependent... It is the maximum amount of time for which we allow the dealdine task to starve non-deadline tasks, so it should be an absolute time, not something HZ-dependent... No?
> Hmm, for HZ=1000 that ends up with a max period of 10ms, that's far > too low, 24Hz needs ~41ms. We can of course also limit the runtime by > capping u for users (as we should anyway).
Regarding capping u for users: some time ago, with Juri we discussed the idea of having per-cgroup limits on the deadline utilization... I think this is a good idea (and if the userspace creates a cgroup per user, this results in per-user capping - but it is more flexible in general)
Luca
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