Messages in this thread |  | | Date | Mon, 19 Dec 2022 12:46:54 +0100 | From | Sebastian Andrzej Siewior <> | Subject | Re: [RFC/RFT PATCH 1/2] sched/core: Check and schedule ksoftirq |
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On 2022-12-19 12:33:22 [+0100], Peter Zijlstra wrote: > ksoftirq is typically a CFS task while idle injection is required to be > a FIFO (typically FIFO-1) task -- so that would require lifting > ksoftirqd to FIFO and that has other problems. > > I'm guessing the problem case is where idle injection comes in while > ksoftirq is running (and preempted), because in that case you cannot run > the softirq stuff in-place. > > The 'right' thing to do would be to PI boost ksoftirqd in that case I > suppose. Perhaps something like so, it would boost ksoftirq when it's > running, and otherwise runs the ksoftirqd thing in-situ. > > I've not really throught hard about this though, so perhaps I completely > wrecked things.
I don't know why you intend to run ksoftirqd but in general it breaks RT left and right and we attempt to avoid running ksoftirqd as much as possible. If it runs and you go and boost it then it probably gets even worse from RT point of view.
ksoftirqd runs softirqs from hardirq context. Everything else is handled in is handled within local-bh-disable+enable loop. We already have have the boost-ksoftird hammer which is the per-CPU BLK called local_bh_disable(). In general everything should be moved out of it. For timers we have the ktimerd thread which needs clean up.
Sebastian
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