[dpdk-dev] [PATCH v3 4/8] raw/ioat: create device on probe and destroy on release

Bruce Richardson bruce.richardson at intel.com
Fri Jun 28 15:15:00 CEST 2019


On Fri, Jun 28, 2019 at 01:59:26PM +0100, Burakov, Anatoly wrote:
> On 28-Jun-19 1:46 PM, Bruce Richardson wrote:
> > On Thu, Jun 27, 2019 at 01:28:04PM +0100, Burakov, Anatoly wrote:
> > > On 27-Jun-19 11:40 AM, Bruce Richardson wrote:
> > > > Add the create/destroy driver functions so that we can actually allocate
> > > > a rawdev and destroy it when done. No rawdev API functions are actually
> > > > implemented at this point.
> > > > 
> > > > Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> > > > ---
> > > 
> > > <snip>
> > > 
> > > > +	rawdev->driver_name = dev->device.driver->name;
> > > > +
> > > > +	ioat = rawdev->dev_private;
> > > > +	ioat->rawdev = rawdev;
> > > > +	ioat->regs = dev->mem_resource[0].addr;
> > > > +	ioat->ring_size = 0;
> > > > +	ioat->desc_ring = NULL;
> > > > +	ioat->status_addr = rte_malloc_virt2iova(ioat) +
> > > > +			offsetof(struct rte_ioat_rawdev, status);
> > > 
> > > While reviewing other patch, i remembered that i've seen this here. You
> > > can't make any guarantees about IOVA addresses in rte_malloc-allocated
> > > memory. Are you sure you don't require IOVA-contiguous memory here?
> > > 
> > Presumably we can guarantee that for structures less than 1 page in size,
> > this will work? I believe the device structure should be within that page
> > limit.
> > 
> 
> No, we can't. That would only be true if you were allocating IOVA-contiguous
> memory. Otherwise there's nothing stopping the allocator to allocate even a
> few kilobytes across page boundary.
> 
> You can only ever guarantee that *one cache line* will not cross the page
> boundary with rte_malloc. With rte_memzone and IOVA_CONTIG flag, you'll be
> able to guarantee IOVA-contiguousness in all cases (or allocation failure).
> 
Ok, so I either need to move this field to the start of the structure, i.e.
have offset zero, or else use contiguous allocation. Will fix in next
version.

/Bruce


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