Re: [PATCH 0/6] support "dataplane" mode for nohz_full

On Mon, 2015-05-11 at 15:25 -0400, Chris Metcalf wrote:

On 05/11/2015 03:19 PM, Mike Galbraith wrote:

quoted

I really shouldn't have acked nohz_full -> isolcpus.  Beside the fact
that old static isolcpus was_supposed_  to crawl off and die, I know
beyond doubt that having isolated a cpu as well as you can definitely
does NOT imply that said cpu should become tickless.

True, at a high level, I agree that it would be better to have a
top-level concept like Frederic's proposed ISOLATION that includes
isolcpus and nohz_cpu (and other stuff as needed).

That said, what you wrote above is wrong; even with the patch you
acked, setting isolcpus does not automatically turn on nohz_full for
a given cpu.  The patch made it true the other way around: when
you say nohz_full, you automatically get isolcpus on that cpu too.
That does, at least, make sense for the semantics of nohz_full.

I didn't write that, I wrote nohz_full implies (spelled '->') isolcpus.
Yes, with nohz_full currently being static, the old allegedly dying but
also static isolcpus scheduler off switch is a convenient thing to wire
the nohz_full CPU SET (<- hint;) property to.

	-Mike