One of these things (CONFIG_HZ) is not like the others..

[Matt Sealey]

On Mon, Jan 21, 2013 at 4:45 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Mon, Jan 21, 2013 at 10:30:07PM +0000, Arnd Bergmann wrote:
>> On Monday 21 January 2013, Matt Sealey wrote:
>> > So is that a bug in that it is not available to ARM right now, a bug
>> > in that it would be impossible for anyone on ARM to have ever tested
>> > this code, or a bug in that it should NEVER be enabled for ARM for
>> > some reason? John? Ingo? :)
>> >
>>
>> I think it's a bug that it's not available. That does not look intentional.
>
> What's a bug?  kernel/Kconfig.hz not being available?  No, it's
> intentional.  (See my replies).

The bug I saw as real is that CONFIG_SCHED_HRTICK is defined only in
kernel/Kconfig.hz (and used in kernel/sched only) - so if we want that
functionality enabled we will also have to opencode it in
arch/arm/Kconfig. Everyone else, by virtue of using kernel/Kconfig.hz,
gets this config item enabled for free if they have hrtimers or
generic smp helpers.. if I understood what John just said, this means
on ARM, since we don't use kernel/Kconfig.hz and we don't also define
an item for CONFIG_SCHED_HRTICK, the process scheduler is completely
oblivious that we're running in HRT mode?

The thing I don't know is real is if that really matters one bit..

-- 
Matt Sealey <matt at genesi-usa.com>
Product Development Analyst, Genesi USA, Inc.