On 26.07.2017 20:49, John David Anglin wrote:
> On 2017-07-26, at 2:02 PM, Helge Deller wrote:
>
>> Instead I'd then suggest the patch below.
>> The if-clause in switch_mm_irqs_off() will then probably be optimized
>> away by the compiler.
>>
>> diff --git a/arch/parisc/include/asm/mmu_context.h b/arch/parisc/include/asm/mmu_context.h
>> index a812262..e4a6570 100644
>> --- a/arch/parisc/include/asm/mmu_context.h
>> +++ b/arch/parisc/include/asm/mmu_context.h
>> @@ -63,6 +63,9 @@ static inline void switch_mm(struct mm_struct *prev,
>> {
>> unsigned long flags;
>>
>> + if (prev == next)
>> + return;
>> +
>> local_irq_save(flags);
>> switch_mm_irqs_off(prev, next, tsk);
>> local_irq_restore(flags);
>
> You are correct. I missed the fact that switch_mm_irqs_off() is used by kernel/sched/core.c.
>
> Maybe we should replace the "switch_mm_irqs_off(prev, next, tsk);" with the mtctl and load_context
> lines to ensure that the if-clause is optimized?
I think we should look at the generated assembly, and if it's not optimized away replace it with mtctl/load_context.
Helge
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