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

[Liang Ma <liangma@liangbit.com>]

On Wed, Apr 07, 2021 at 10:43:36AM +0200, Thomas Monjalon wrote:
> +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.
+1 that's ineresting to have a abstract layer of DMA offload engine. 
   I would like join the discussion. please add me in the cc list in the
   new 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?
> 
> 
>