Re: [PATCH 2/6] sched/preempt: refactor sched_dynamic_update()

Frederic Weisbecker
2022-02-03T11:53:39Z

On Wed, Feb 02, 2022 at 06:08:27PM +0000, Mark Rutland wrote:
> On Wed, Feb 02, 2022 at 05:01:44PM +0100, Frederic Weisbecker wrote:
> > On Wed, Feb 02, 2022 at 03:13:57PM +0000, Mark Rutland wrote:
> > > > > +#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace_thunk
> > > > > +#define preempt_schedule_notrace_dynamic_disabled NULL
> > > >
> > > > I'm worried about un-greppable macro definitions like this.
> > > I assume you mean that it's hard to go from:
> > >
> > > preempt_dynamic_enable(preempt_schedule_notrace);
> > >
> > > ... to this, because the `_dynamic_enabled` or `_dynamic_disabled` part gets
> > > token-pasted on?
> >
> > Right.
>
> Looking at this some more, I'm probably going to need to do token-pasting at
> some level no matter what we do, so how big of a concern is this? Searching
> for 'foo_function' should also find 'foo_function_dynamic_enabled' and
> 'foo_function_dynamic_disabled', and searching for either of those will find
> their original definition.
>
> If others aren't concerned, could we just live with that for now?

Sure, I don't have a better idea right now. I'll try to think of something
after the next iteration.

> > I was hoping to make a default backend based on static keys to implement these
> > toggeable static calls, but I had some issues on the way, although I can't
> > remember exactly which.
> >
> > So eventually I don't know if this stuff will be useful for you....
>
> Having had a play with this, since you need to generate a wrapper for the
> static_key case, you either need to match the prototype or have a generic
> macro (and you likely end up back in token-pasting hell again anyhow).
>
> So as above, how much does this matter for now?
>
> > Well, I guess this can still ease a wrapper like:
> >
> > preempt_dynamic_enable(sym)
> > ---> CONFIG_STATIC_CALL=y? -----> static_call_enable(sym)
> > else
> > ---> CONFIG_STATIC_KEY=y? -----> static_key_enable(sym)
>
> In this series I just define preempt_dynamic_enable() dependent on
> CONFIG_STATIC_CALL or CONFIG_STATIC_KEY, which is functionally equivalent.

You're right.

It's just that instead of:

#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#ifndef preempt_schedule_notrace_dynamic_enabled
#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace
#define preempt_schedule_notrace_dynamic_disabled NULL
#endif

#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled)
#define preempt_dynamic_disable(f) static_call_update(f, #f##_dynamic_disabled)

You have:

DECLARE_STATIC_CALL_TOGGLE(preempt_schedule_notrace, __preempt_schedule_notrace_func);

#define preempt_dynamic_enable(f) static_call_enable(f)
#define preempt_dynamic_disable(f) static_call_disable(f)

Thanks.