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

[Burakov, Anatoly]

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).

-- 
Thanks,
Anatoly