[RFC/PATCH 5/7] ARM: Move get_thread_info macro definition to <asm/assembler.h>

[George G. Davis]

On Oct 13, 2011, at 10:34 AM, Russell King - ARM Linux wrote:

> On Wed, Oct 12, 2011 at 02:04:33AM -0400, gdavis at mvista.com wrote:
>> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
>> index 78397d0..eaf4939 100644
>> --- a/arch/arm/include/asm/assembler.h
>> +++ b/arch/arm/include/asm/assembler.h
>> @@ -36,6 +36,20 @@
>> 	.endm
>> #endif  /* !CONFIG_THUMB2_KERNEL */
>> 
>> +	.macro	preempt_disable, tsk, cnt
>> +	get_thread_info \tsk
>> +	ldr	\cnt, [\tsk, #TI_PREEMPT]
>> +	add	\cnt, \cnt, #1
>> +	str	\cnt, [\tsk, #TI_PREEMPT]
>> +	.endm
>> +
>> +	.macro	preempt_enable, tsk, cnt
>> +	get_thread_info \tsk
>> +	ldr	\cnt, [\tsk, #TI_PREEMPT]
>> +	sub	\cnt, \cnt, #1
>> +	str	\cnt, [\tsk, #TI_PREEMPT]
>> +	.endm
>> +
>> /*
>>  * Endian independent macros for shifting bytes within registers.
>>  */
>> 
>> 
>> Not as efficient as it could be but I imagine the macros could
>> be written to support optional load of \tsk and/or optional \tmp
>> parameters to cover other common cases.
> 
> It's actually not that simple either: if you disable preemption, then you
> need to check for a preempt event after re-enabling preemption.  The
> C level code does this:
> 
> #define preempt_enable_no_resched() \
> do { \
>        barrier(); \
>        dec_preempt_count(); \
> } while (0)
> 
> #define preempt_check_resched() \
> do { \
>        if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
>                preempt_schedule(); \
> } while (0)
> 
> #define preempt_enable() \
> do { \
>        preempt_enable_no_resched(); \
>        barrier(); \
>        preempt_check_resched(); \
> } while (0)
> 
> Note that preempt_schedule() will check the preempt count itself and
> return immediately if non-zero or irqs are disabled.

It would be easier to just insert preempt_disable/preempt_enable in
the cache and proc function call macros.  I did that in an earlier test
patch but moved it into the cache-v6.S and proc-v6.S files instead
since it only affects ARM11 MPCore as far as I'm aware.

--
Regards,
George