Messages in this thread | | | Subject | Re: [patchlet] sched: fix rt throttle runtime borrowing | From | Peter Zijlstra <> | Date | Tue, 08 Mar 2011 14:46:23 +0100 |
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On Tue, 2011-03-08 at 14:27 +0100, Mike Galbraith wrote:
> > Also, how much of a problem is it really? When I start a FIFO spinner on > > my machine I can still ssh in and kill the thing. > > It's a problem if you have one box. Also, try starting a hefty load > then having an rt task go nuts. Nothing good happens here.
Right, so I think we're not aggressive enough to migrate tasks away from very small cpu_power CPUs, trapping tasks on such CPUs.
Of course, this is no help for pinned tasks.. but then you get what you asked for isn't it ;-)
> > Not allowing 100% FIFO usage on SMP is going to make it very very hard > > to implement any kind of fifo-cgroup stuff. > > The only thing I care much about is the default setup. The safety net > should work, otherwise it's a waste.
Right, but how much trouble can be avoided by making the sched_fair load-balancer migrate tasks away from very small cpu_power CPUs?
It won't avoid actual deadlocks when someone tries to wait for workqueue broadcasts and the like, but how much of that is actually happening?
> Maybe only doing the borrow thing when there are active RT groups is the > right thing to do. (minus knob)
Thing is the whole borrowing needs to go, Dario and me finally came up with a 'sane' way to implement fifo-cgroups, but that does include explicitly allowing starving CPUs.
Not allowing that very quickly degenerates into massive trouble like gang-scheduling or bouncing tasks around like mad and generally messing up the 'load-balancer'.
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