Re: [dpdk-dev] [PATCH v3 2/4] kni: fix kni fifo synchronization

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/10/2018 11:06 AM, Gavin Hu (Arm Technology China) wrote:
> 
> 
>> -----Original Message-----
>> From: Phil Yang (Arm Technology China)
>> Sent: Wednesday, October 10, 2018 5:59 PM
>> To: Stephen Hemminger <stephen@networkplumber.org>
>> Cc: dev@dpdk.org; jerin.jacob@caviumnetworks.com; Gavin Hu (Arm
>> Technology China) <Gavin.Hu@arm.com>; Honnappa Nagarahalli
>> <Honnappa.Nagarahalli@arm.com>; Ola Liljedahl <Ola.Liljedahl@arm.com>;
>> ferruh.yigit@intel.com
>> Subject: RE: [dpdk-dev] [PATCH v3 2/4] kni: fix kni fifo synchronization
>>
>> Hi Hemminger,
>>
>>> -----Original Message-----
>>> From: Stephen Hemminger <stephen@networkplumber.org>
>>> Sent: Tuesday, October 9, 2018 5:53 AM
>>> To: Phil Yang (Arm Technology China) <Phil.Yang@arm.com>
>>> Cc: dev@dpdk.org; jerin.jacob@caviumnetworks.com; Gavin Hu (Arm
>>> Technology China) <Gavin.Hu@arm.com>; Honnappa Nagarahalli
>>> <Honnappa.Nagarahalli@arm.com>; Ola Liljedahl <Ola.Liljedahl@arm.com>;
>>> ferruh.yigit@intel.com
>>> Subject: Re: [dpdk-dev] [PATCH v3 2/4] kni: fix kni fifo
>>> synchronization
>>>
>>> On Mon,  8 Oct 2018 17:11:44 +0800
>>> Phil Yang <phil.yang@arm.com> wrote:
>>>
>>>> diff --git a/lib/librte_kni/rte_kni_fifo.h
>>>> b/lib/librte_kni/rte_kni_fifo.h index ac26a8c..70ac14e 100644
>>>> --- a/lib/librte_kni/rte_kni_fifo.h
>>>> +++ b/lib/librte_kni/rte_kni_fifo.h
>>>> @@ -28,8 +28,9 @@ kni_fifo_put(struct rte_kni_fifo *fifo, void
>>>> **data, unsigned num)  {
>>>>  unsigned i = 0;
>>>>  unsigned fifo_write = fifo->write;
>>>> -unsigned fifo_read = fifo->read;
>>>>  unsigned new_write = fifo_write;
>>>> +rte_smp_rmb();
>>>> +unsigned fifo_read = fifo->read;
>>>>
>>>
>>> The patch makes sense, but this function should be changed to match
>>> kernel code style.
>>> That means no declarations after initial block, and use 'unsigned int'
>>> rather than 'unsigned'
>>>
>>> Also. why is i initialized? Best practice now is to not do gratitious
>>> initialization since it defeats compiler checks for accidental  use of
>> uninitialized variables.
>>>
>>> What makes sense is something like:
>>>
>>> kni_fifo_put(struct rte_kni_fifo *fifo, void **data, unsigned num) {
>>> unsigned int i, fifo_read, fifo_write, new_write;
>>>
>>> fifo_write = fifo->write;
>>> new_write = fifo_write;
>>> rte_smb_rmb();
>>> fifo_read = fifo->read;
>>>
>>> Sorry, blaming you for issues which are inherited from original KNI code.
>>> Maybe someone should run kernel checkpatch (not DPDK checkpatch) on it
>>> and fix those.
>>
>> Thanks for your comment.
>>
>> I think I can submit a new separate patch to fix this historical issue.
>>
>> Thanks,
>> Phil Yang
> 
> I advised a separate patch to make this patch to the point and clean.

+1 to separate patch for clean up.