Finishing off cpumask...

Finishing off cpumask...

[Rusty Russell]

I have had five final cpumask patches in my queue for over a year now, and
I'd like to merge them *next* merge window (not this one, too late).

The first two finally convert mm_struct and task_struct to variable cpumasks,
which are the last in the core kernel.  The next two turn off and break
old-style cpumask uses when CONFIG_CPUMASK_OFFSTACK is set, and the final one
actually means we don't allocate all NR_CPUS bits for bitmasks.

Historically, this stuff has revealed issues when turned on, so I'd like it
to have a long baking cycle in Ingo's tree and big-machine testers.

I'm rebasing and retesting now, will post git tree when I have it.

Thanks,
Rusty.

Re: Finishing off cpumask...

[Peter Zijlstra]

On Thu, 2010-10-21 at 17:35 +1030, Rusty Russell wrote:
> The next two turn off and break
> old-style cpumask uses when CONFIG_CPUMASK_OFFSTACK is set, 

Breaking old style for !CONFIG_CPUMASK_OFFSTAK too would be awesome, but
I guess that's hard to do?

Re: Finishing off cpumask...

[Rusty Russell]

On Thu, 21 Oct 2010 07:51:47 pm Peter Zijlstra wrote:
> On Thu, 2010-10-21 at 17:35 +1030, Rusty Russell wrote:
> > The next two turn off and break
> > old-style cpumask uses when CONFIG_CPUMASK_OFFSTACK is set, 
> 
> Breaking old style for !CONFIG_CPUMASK_OFFSTAK too would be awesome, but
> I guess that's hard to do?

There are four things we could do.
(1) Get rid of the old cpus_ operators (=> cpumask_*).  They're just
    confusing, and  removing them would be a clarity win.
(2) Get rid of cpu_*_map (=> cpu_*_mask).  The maps are just wrappers.
(3) Getting rid of cpumask_t (=> struct cpumask) and NR_CPUS
    (=> CONFIG_NR_CPUS). These are totally cosmetic.
(4) Getting rid of cpumask_t/struct cpumask (=> cpumask_var_t) is basically
    only useful if an arch is thinking about CPUMASK_OFFSTACK, and most
    painful.

So, I've changed the CONFIG option which disables (1) and (2); now anyone
will be able to turn it on if they want to test.  That might encourage
the per-arch cleanup...

Thanks,
Rusty.