Messages in this thread | | | Date | Fri, 20 Nov 2015 11:58:12 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH 3/4] sched: introduce synchronized idle injection |
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On Fri, 20 Nov 2015, Peter Zijlstra wrote:
> On Fri, Nov 20, 2015 at 10:45:14AM +0100, Thomas Gleixner wrote: > > > The whole concept of faking idle is simply crap. > > :-) > > > If you want to avoid that stuff in the scheduler, then create a > > mechanism which just defers the next timer interrupt for X > > milliseconds and does not any fiddling with NOHZ state and such. > > Not sure that will actually result in the machine going idle. Device > interrupts will still wake tasks and get them ran.
That's not what I meant. If you don't want to control all that from the scheduler than you are back to that thread which "runs" at RT priority and does
if (machine_on_fire) { defer_timer_interrupt(5ms); end = now + 5ms: while (now < end) mwait(); }
That's what the existing code does, but the above does not longer claim it's idle and confuses the hell out of nohz and whatever. It's just a "runaway" RT task which "hogs" the CPU for 5ms and makes the next timer interrupt firing late.
Thanks,
tglx
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