Re: sched/fair: Long delays starting RT processes on idle cpu.

[Steven Rostedt]

On Mon, 27 Jan 2020 15:39:24 +0000
David Laight <David.Laight@xxxxxxxxxx> wrote:

> I'd have thought that the processor should wake up much faster than that.
> I can't see the memory write that is paired with the monitor/mwait.
> Does it need a strong barrier?

You may want to prevent the CPU from going into a deep C state. 90us is
something I would expect if the CPU is in a deep C state (I've seen
much longer wake up times due to deep C state).

Boot the kernel with idle=poll and see if you can trigger the same
latency. If not, then you know it's the CPU going into a deep C state
that is causing your latency.

-- Steve