Re: [PATCH v10 05/12] task_isolation: support CONFIG_TASK_ISOLATION_ALL

[Ingo Molnar <mingo@kernel.org>]

* Chris Metcalf <cmetcalf@mellanox.com> wrote:

> On 03/03/2016 01:34 PM, Andi Kleen wrote:
> >Chris Metcalf <cmetcalf@ezchip.com> writes:
> >>+config TASK_ISOLATION_ALL
> >>+	bool "Provide task isolation on all CPUs by default (except CPU 0)"
> >>+	depends on TASK_ISOLATION
> >>+	help
> >>+	 If the user doesn't pass the task_isolation boot option to
> >>+	 define the range of task isolation CPUs, consider that all
> >>+	 CPUs in the system are task isolation by default.
> >>+	 Note the boot CPU will still be kept outside the range to
> >>+	 handle timekeeping duty, etc.
> >That seems like a very dangerous Kconfig option.
> >"CONFIG_BREAK_EVERYTHING"
> >If someone sets that by default they will have a lot of trouble.
> >
> >I wouldn't add that, make it a run time option only.
> 
> So you were thinking, allow a special boot syntax "task_isolation=all",
> which puts all the cores into task isolation mode except the boot core?
> 
> My original argument was that it was so parallel to the existing
> CONFIG_NO_HZ_FULL_ALL option that it just made sense to do it,
> and some testers complained about having to specify the precise
> cpu range, so this seemed like an easy fix.

Yes, it's absolutely legitimate to offer boot options as Kconfig options as well - 
in fact that will get things like randconfig bootups stumble upon them and do some 
free testing for you. Just ignore Andi's nonsensical objection.

One day we'll have a unified boot parameter/Kconfig/sysctl mechanism, so that it 
will be possible to say things like this on the boot command line:

  CONFIG_NO_HZ_FULL_ALL=y

... which will eliminate quite a bit of the current schizm between Kconfig and 
boot time parameters.

Thanks,

	Ingo