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

Thomas Gleixner
2020-11-16T17:43:27Z

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 ...

Thanks,

tglx