Re: [dpdk-dev] [PATCH] eal: force IOVA mode to physical

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 06-Sep-18 8:34 AM, Jerin Jacob wrote:
> -----Original Message-----
>> Date: Tue, 4 Sep 2018 23:40:36 -0400
>> From: Eric Zhang <eric.zhang@windriver.com>
>> To: santosh <santosh.shukla@caviumnetworks.com>, hemant.agrawal@nxp.com,
>>   Gaëtan Rivet <gaetan.rivet@6wind.com>, "Burakov, Anatoly"
>>   <anatoly.burakov@intel.com>
>> CC: bruce.richardson@intel.com, dev@dpdk.org, Allain.Legacy@windriver.com,
>>   Matt.Peters@windriver.com
>> Subject: Re: [dpdk-dev] [PATCH] eal: force IOVA mode to physical
>> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
>>   Thunderbird/52.9.1
>>
>> On 08/30/2018 08:59 AM, santosh wrote:
>>> On Thursday 30 August 2018 05:43 PM, Hemant wrote:
>>>> External Email
>>>>
>>>> Hi,
>>>>
>>>> On 8/30/2018 3:13 PM, Gaëtan Rivet wrote:
>>>>> Hi,
>>>>>
>>>>> On Thu, Aug 30, 2018 at 10:09:04AM +0100, Burakov, Anatoly wrote:
>>>>>> On 29-Aug-18 4:58 PM, eric zhang wrote:
>>>>>>> This patch adds a configuration option to force the IOVA mode to
>>>>>>> physical address (PA). There exists virtual devices that are not
>>>>>>> directly attached to the PCI bus, and therefore the auto detection
>>>>>>> of the IOVA mode based on probing the PCI bus and IOMMU configuration
>>>>>>> may not report the required addressing mode. Having the configuration
>>>>>>> option permits the mode to be explicitly configured in this scenario.
>>>>>>>
>>>>>>> Signed-off-by: eric zhang <eric.zhang@windriver.com>
>>>>>>> ---
>>>>>> Defining this at compile-time seems like an overkill. Wouldn't it be better
>>>>>> to just add an EAL command-line option to force IOVA mode to a particular
>>>>>> value?
>>>> That is a good suggestion.
>>>>>> --
>>>>>> Thanks,
>>>>>> Anatoly
>>>>> What is the bus of these devices and why not implement get_iommu_class
>>>>> in it?
>>>> There are cases, where you are using dpdk libraries with external
>>>> libraries and you need to change the default behavior DPDK lib to use
>>>> physical address instead of virtual address.
>>>> Providing an option to user will help.
>>>>
>>>>
>>> More appropriate solution could be:
>>> * Either fix it at bus layer .. i.e.. get_iommu_class()..
>>> * Or introduce something like [1] --iova-mode=<pa/va> param.
>>>
>>> Former is better solution than latter if autodetection is a key criteria.
>>> Thanks.
>>>
>>> [1] http://patchwork.dpdk.org/patch/25192/
>>>
>> It's not generic which couldn't be fixed at bus layer.
>> So what's the preference of EAL option or compile time solution?
>> Adding --iova-mode as patch [1] will overrivde auto-detection
>> rte_bus_get_iommu_class()
>> make it no use; compile time solution will align with upstream and keep
>> new atuodetection
>> solution in #ifndef.
> 
> If it is for vdev devices, why not introduce something like
> RTE_PCI_DRV_IOVA_AS_VA and let vdev device describe its personality.
> And based on the devices(flags) on vdev bus, rte_bus_get_iommu_class()
> of vdev can decide the mode just like PCI bus.
> 

That seems like a better option to me, +1. As far as i know, at the 
moment if there are no devices attached at all, or if there are only 
vdev devices attached, DPDK will default to IOVA as PA mode for no good 
reason; such a change would certainly fix this.

> 
>>
>> Thanks
>> Eric
>>
> 


-- 
Thanks,
Anatoly