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

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

[Cheng Jiang]

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;
 		dma_info->nr++;
 		i++;
 	}
-- 
2.29.2

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

[Hu, Jiayu]

Reviewed-by: Jiayu Hu <jiayu.hu@intel.com>

> -----Original Message-----
> From: Jiang, Cheng1 <cheng1.jiang@intel.com>
> Sent: Wednesday, March 17, 2021 1:41 PM
> To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Yang, YvonneX
> <yvonnex.yang@intel.com>; Wang, Yinan <yinan.wang@intel.com>; Jiang,
> Cheng1 <cheng1.jiang@intel.com>; stable@dpdk.org
> Subject: [PATCH] examples/vhost: fix ioat ring space in callbacks
> 
> 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;
>  		dma_info->nr++;
>  		i++;
>  	}
> --
> 2.29.2

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

[Maxime Coquelin]

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?

>  		dma_info->nr++;
>  		i++;
>  	}
> 

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

[Hu, Jiayu]

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/

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

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

[Thomas Monjalon]

07/04/2021 09:47, Maxime Coquelin:
> 
> 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?

Having a generic DMA API may be interesting.
Do you know any other HW candidate for such an API?
Do you think rte_memcpy can be used as a SW driver?

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

[Thomas Monjalon]

+Cc more people to start a discussion about a potential DMA API.
If you think it is interesting, we can start a fresh discussion thread.

07/04/2021 10:26, Thomas Monjalon:
> 07/04/2021 09:47, Maxime Coquelin:
> > 
> > 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.
[...]
> > > --- 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?
> 
> Having a generic DMA API may be interesting.
> Do you know any other HW candidate for such an API?
> Do you think rte_memcpy can be used as a SW driver?

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

[Maxime Coquelin]

On 4/7/21 10:26 AM, Thomas Monjalon wrote:
> 07/04/2021 09:47, Maxime Coquelin:
>>
>> 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?
> 
> Having a generic DMA API may be interesting.
> Do you know any other HW candidate for such an API?
> Do you think rte_memcpy can be used as a SW driver?

Yes, I guess we could create a vdev driver with MEM_TO_MEM capability
using rte_memcpy().

Note that IOAT in the Kernel is supported by the DMA framework.

Regards,
Maxime