[dpdk-dev] Why do we need iommu=pt?

[Shivapriya Hiremath]

Hi,

Thank you for all the replies.
I am trying to understand the impact of this on DPDK. What will be the
repercussions of disabling "iommu=pt" on the DPDK performance?


On Tue, Oct 21, 2014 at 12:32 AM, Alex Markuze <alex at weka.io> wrote:

> DPDK uses a 1:1 mapping and doesn't support IOMMU.  IOMMU allows for
> simpler VM physical address translation.
> The second role of IOMMU is to allow protection from unwanted memory
> access by an unsafe devise that has DMA privileges. Unfortunately this
> protection comes with an extremely high performance costs for high speed
> nics.
>
> To your question iommu=pt disables IOMMU support for the hypervisor.
>
> On Tue, Oct 21, 2014 at 1:39 AM, Xie, Huawei <huawei.xie at intel.com> wrote:
>
>>
>>
>> > -----Original Message-----
>> > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Shivapriya
>> Hiremath
>> > Sent: Monday, October 20, 2014 2:59 PM
>> > To: dev at dpdk.org
>> > Subject: [dpdk-dev] Why do we need iommu=pt?
>> >
>> > Hi,
>> >
>> > My question is that if the Poll mode  driver used the DMA kernel
>> interface
>> > to set up its mappings appropriately, would it still require that
>> iommu=pt
>> > be set?
>> > What is the purpose of setting iommu=pt ?
>> PMD allocates memory though hugetlb file system, and fills the physical
>> address
>> into the descriptor.
>> pt is used to pass through iotlb translation. Refer to the below link.
>> http://lkml.iu.edu/hypermail/linux/kernel/0906.2/02129.html
>> >
>> > Thank you.
>>
>
>