Re: [PATCH 0/3] nohz: Convert tick dependency mask to atomic_t

[Ingo Molnar <mingo@kernel.org>]

* Ingo Molnar <mingo@kernel.org> wrote:

> That's a totally useless analysis of task_struct::flags, while we want to 
> convert thread_info::flags...

So going over to arguing about thread_info::flags:

1)

We already have ti::flags accessors for most of the generic code. There's a few 
outliers (in the scheduler code...) which can be fixed.

2)

We could introduce a ARCH_HAS_ATOMIC_TIF flag to do per arch conversion: this 
would trigger #ifdefs in the accessors. When an architecture switches ti::flags to 
atomic_t, it also sets ARCH_HAS_ATOMIC_TIF.

I'd still do a flags => __flags rename of the field, to make the conversion easy 
and safe. So any arch that has ARCH_HAS_ATOMIC_TIF set provides an atomic_t 
thread_info::__flags field.

3)

The new accessors under ARCH_HAS_ATOMIC_TIF would use atomic.h functions to 
shuffle the thread-info flags.

4)

After one kernel release we could add:

	WARN_ONCE("please convert thread_info::flags to atomic_t!", 1);

to the old accessors to accelerate conversion.

5)

Eventually, once every architecture is converted, we could eliminate the old 
sched.c fetch_or() macro.

Thanks,

	Ingo