Re: [dpdk-dev] [PATCH 1/3] eal/arm64: remove the braces {} for dmb(), dsb()

[Jia He <hejianet@gmail.com>]

On 11/9/2017 5:38 PM, Ananyev, Konstantin Wrote:
>
>> -----Original Message-----
>> From: Jianbo Liu [mailto:jianbo.liu@arm.com]
>> Sent: Thursday, November 9, 2017 4:56 AM
>> To: Jia He <hejianet@gmail.com>
>> Cc: Richardson, Bruce <bruce.richardson@intel.com>; jerin.jacob@caviumnetworks.com; dev@dpdk.org; olivier.matz@6wind.com;
>> Ananyev, Konstantin <konstantin.ananyev@intel.com>; hemant.agrawal@nxp.com; jia.he@hxt-semitech.com
>> Subject: Re: [PATCH 1/3] eal/arm64: remove the braces {} for dmb(),dsb()
>>
>> The 11/09/2017 12:43, Jia He wrote:
>>> Hi Jianbo
>>>
>>>
>>> On 11/9/2017 11:21 AM, Jianbo Liu Wrote:
>>>> The 11/09/2017 11:14, Jia He wrote:
>>>>> On 11/9/2017 9:22 AM, Jia He Wrote:
>>>>>> Hi Bruce
>>>>>>
>>>>>>
>>>>>> On 11/8/2017 6:28 PM, Bruce Richardson Wrote:
>>>>>>> On Wed, Nov 08, 2017 at 06:17:10AM +0000, Jia He wrote:
>>>>>>>> for the code as follows:
>>>>>>>> if (condition)
>>>>>>>>      rte_smp_rmb();
>>>>>>>> else
>>>>>>>>      rte_smp_wmb();
>>>>>>>> Without this patch, compiler will report this error:
>>>>>>>> error: 'else' without a previous 'if'
>>>>>>>>
>>>>>>>> Signed-off-by: Jia He <hejianet@gmail.com>
>>>>>>>> Signed-off-by: jia.he@hxt-semitech.com
>>>>>>>> ---
>>>>>>>>    lib/librte_eal/common/include/arch/arm/rte_atomic_64.h | 4 ++--
>>>>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>>>
>>>>>>>> diff --git
>>>>>>>> a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
>>>>>>>> b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
>>>>>>>> index 0b70d62..38c3393 100644
>>>>>>>> --- a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
>>>>>>>> +++ b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
>>>>>>>> @@ -43,8 +43,8 @@ extern "C" {
>>>>>>>>      #include "generic/rte_atomic.h"
>>>>>>>>    -#define dsb(opt)  { asm volatile("dsb " #opt : : : "memory"); }
>>>>>>>> -#define dmb(opt)  { asm volatile("dmb " #opt : : : "memory"); }
>>>>>>>> +#define dsb(opt) asm volatile("dsb " #opt : : : "memory");
>>>>>>>> +#define dmb(opt) asm volatile("dmb " #opt : : : "memory");
>>>>>>> Need to remove the trailing ";" I too I think.
>>>>>>> Alternatively, to keep the braces, the standard practice is to use
>>>>>>> do { ... } while(0)
>>>>>> If trailing ";" is not removed
>>>>>> the code:
>>>>>> if (condition)
>>>>>>      rte_smp_rmb();
>>>>>> else
>>>>>>      anything();
>>>>>>
>>>> Sorry, why not use two different functions as your conditions passed in
>>>> are fixed in the calling functions.
>>> Do you mean to split update_tail() into update_tail_enqueue() and
>>> update_tail_dequeue()?
>> Yes. So it's not need to change dsb/dmb.
> That's a good idea - but you still might hit the same problem in
> Some different place in future...
> Why not to convert these macros into 'always_inline' functions then?
> Konstantin
>
It makes things more complex
opt needs to be redefined with types
such as : __attribute__((always_inline)) void dsb( char* opt)
and the input paramenter shoud be
#define sy "sy"
#define ld "ld"

And the "#" in asm codes needs to be considerred more.

IMO, the kernel way is simple and clean, isn't it?
#define dmb(opt) asm volatile("dmb " #opt : : : "memory")
Another choice is adding the do/while.

@Ananyev @Jianbo
Any thoughts?

-- 
Cheers,
Jia