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

From: Chris Metcalf
Date: Mon May 11 2015 - 15:25:45 EST

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

Chris Metcalf, EZChip Semiconductor

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