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

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  Re: [PATCH v10 05/12] task_isolation: support CONFIG_TASK_ISOLATION_ALL Andi Kleen <andi@firstfloor.org> - 2016-03-03 19:40 +0100
    Re: [PATCH v10 05/12] task_isolation: support  CONFIG_TASK_ISOLATION_ALL Andi Kleen <andi@firstfloor.org> - 2016-03-03 21:10 +0100
    Re: [PATCH v10 05/12] task_isolation: support  CONFIG_TASK_ISOLATION_ALL Ingo Molnar <mingo@kernel.org> - 2016-03-05 13:40 +0100

#1349475 — Re: [PATCH v10 05/12] task_isolation: support CONFIG_TASK_ISOLATION_ALL

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.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only

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#1349543 — Re: [PATCH v10 05/12] task_isolation: support CONFIG_TASK_ISOLATION_ALL

> The same arguments would seem to apply to TASK_ISOLATION_ALL;
> note that applications don't actually go into task isolation mode
> without issuing the appropriate prctl(), so it shouldn't be too

That's a fair point. If it's entirely opt-in it's probably ok.

-Andi

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#1350885 — Re: [PATCH v10 05/12] task_isolation: support CONFIG_TASK_ISOLATION_ALL

* 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

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