Re: [patch 10/19] preempt: Cleanup the macro maze a bit

Peter Zijlstra
2020-11-17T10:22:15Z

On Mon, Nov 16, 2020 at 06:42:19PM +0100, Thomas Gleixner wrote:
> On Mon, Nov 16 2020 at 13:17, Peter Zijlstra wrote:
> > On Fri, Nov 13, 2020 at 03:02:17PM +0100, Thomas Gleixner wrote:
> >
> >> -#define irq_count() (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
> >> - | NMI_MASK))
> >> +#define irq_count() (nmi_count() | hardirq_count() | softirq_count())
> >
> >
> >> +#define in_task() (!(in_nmi() | in_hardirq() | in_serving_softirq()))
> >> -#define in_task() (!(preempt_count() & \
> >> - (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
> >
> > How horrible is the code-gen? Because preempt_count() is
> > raw_cpu_read_4() and at least some old compilers will refuse to CSE it
> > (consider the this_cpu_read_stable mess).
>
> I looked at gcc8 and 10 output and the compilers are smart enough to
> fold it for the !RT case. But yeah ...

If recent GCC is smart enough I suppose it doesn't matter, thanks!