Re: [dpdk-dev] [PATCH] examples/vhost: fix ioat ring space in callbacks

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 4/7/21 9:54 AM, Hu, Jiayu wrote:
> Hi Maxime,
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: Wednesday, April 7, 2021 3:48 PM
>> To: Jiang, Cheng1 <cheng1.jiang@intel.com>; Xia, Chenbo
>> <chenbo.xia@intel.com>; Thomas Monjalon <thomas@monjalon.net>
>> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Yang, YvonneX
>> <yvonnex.yang@intel.com>; Wang, Yinan <yinan.wang@intel.com>;
>> stable@dpdk.org
>> Subject: Re: [PATCH] examples/vhost: fix ioat ring space in callbacks
>>
>>
>>
>> On 3/17/21 6:40 AM, Cheng Jiang wrote:
>>> We use ioat ring space for determining if ioat callbacks can enqueue a
>>> packet to ioat device. But there is one slot can't be used in ioat
>>> ring due to the ioat driver design, so we need to reduce one slot in
>>> ioat ring to prevent ring size mismatch in ioat callbacks.
>>>
>>> Fixes: 2aa47e94bfb2 ("examples/vhost: add ioat ring space count and
>> check")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Cheng Jiang <Cheng1.jiang@intel.com>
>>> ---
>>>  examples/vhost/ioat.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/examples/vhost/ioat.c b/examples/vhost/ioat.c
>>> index 60b73be93..9cb5e0d50 100644
>>> --- a/examples/vhost/ioat.c
>>> +++ b/examples/vhost/ioat.c
>>> @@ -113,7 +113,7 @@ open_ioat(const char *value)
>>>  			goto out;
>>>  		}
>>>  		rte_rawdev_start(dev_id);
>>> -		cb_tracker[dev_id].ioat_space = IOAT_RING_SIZE;
>>> +		cb_tracker[dev_id].ioat_space = IOAT_RING_SIZE - 1;
>>
>> That really comforts me in thinking we need a generic abstraction for
>> DMA devices. How is the application developer supposed to know that
>> the DMA driver has such weird limitations?
>>
>> Can the driver be fixed to have a proper behavior?
> 
> Here is the patch of providing capacity check API for DMA:
> http://patches.dpdk.org/project/dpdk/patch/20210318182042.43658-6-bruce.richardson@intel.com/

OK, thanks for the pointer.

While this new API is being reviewed, and for LTS, let's pick your
patch. As soon as Bruce patch is merged, please send a new patch on top
to make use of this API.

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime

> Thanks,
> Jiayu
>>
>>>  		dma_info->nr++;
>>>  		i++;
>>>  	}
>>>
>