Subject: Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

From: Valentine <[email-masked]>
Date: Thu, 29 Oct 2009 00:28:01 +0300

Benjamin Herrenschmidt wrote:
> On Wed, 2009-10-28 at 22:19 +0300, Valentine wrote:
> 
>> I'm just not sure that we need to clear HARDIRQEN here, since we don't 
>> really hard-disable the the interrupts.
> 
> We do, or rather, we come in with the interrupts hard disabled, no ?

Yes, looks like the interrupts are disabled at this point (before 
preempt_schedule_irq) most of the times, but we don't hard-disable them 
here. We just soft-disable them to make preempt_schedule_irq happy. Even 
if an interrupt fires, it will be hard-disabled and the hardirq flag 
will be cleared by the exception handler right away. I just think that 
there's no need to clear hardirq flag if we don't clear MSR_EE.

Thanks,
Val.
> 
> Ben.
> 
>> Thanks,
>> Val.
>>
>>> +	TRACE_DISABLE_INTS
>>> +
>>> +	/* Call the scheduler with soft IRQs off */
>>> +1:	bl	.preempt_schedule_irq
>>> +
>>> +	/* Hard-disable interrupts again (and update PACA) */
>>>  #ifdef CONFIG_PPC_BOOK3E
>>> -	wrteei	1
>>> -	bl	.preempt_schedule
>>>  	wrteei	0
>>>  #else
>>> -	ori	r10,r10,MSR_EE
>>> -	mtmsrd	r10,1		/* reenable interrupts */
>>> -	bl	.preempt_schedule
>>>  	mfmsr	r10
>>> -	clrrdi	r9,r1,THREAD_SHIFT
>>> -	rldicl	r10,r10,48,1	/* disable interrupts again */
>>> +	rldicl	r10,r10,48,1
>>>  	rotldi	r10,r10,16
>>>  	mtmsrd	r10,1
>>>  #endif /* CONFIG_PPC_BOOK3E */
>>> +	li	r0,0
>>> +	stb	r0,PACAHARDIRQEN(r13)
>>> +
>>> +	/* Re-test flags and eventually loop */
>>> +	clrrdi	r9,r1,THREAD_SHIFT
>>>  	ld	r4,TI_FLAGS(r9)
>>>  	andi.	r0,r4,_TIF_NEED_RESCHED
>>>  	bne	1b
>>>  	b	restore
>>>  
>>>  user_work:
>>> -#endif
>>> +#endif /* CONFIG_PREEMPT */
>>> +
>>>  	/* Enable interrupts */
>>>  #ifdef CONFIG_PPC_BOOK3E
>>>  	wrteei	1
> 
>