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From: Alex Markuze <alex@weka.io>
To: "Xie, Huawei" <huawei.xie@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] Why do we need iommu=pt?
Date: Tue, 21 Oct 2014 10:32:08 +0300
Message-ID: <CAKfHP0U-v2fLQwyEa3KBZs3kXpVMQdLU+WgLzQq6xxmrb3Brtg@mail.gmail.com> (raw)
In-Reply-To: <C37D651A908B024F974696C65296B57B0F2CD832@SHSMSX101.ccr.corp.intel.com>

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@intel.com> wrote:

>
>
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Shivapriya Hiremath
> > Sent: Monday, October 20, 2014 2:59 PM
> > To: dev@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.
>

  reply	other threads:[~2014-10-21  7:23 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-20 21:58 Shivapriya Hiremath
2014-10-20 22:39 ` Xie, Huawei
2014-10-21  7:32   ` Alex Markuze [this message]
2014-10-21 16:53     ` Shivapriya Hiremath
2014-10-21 19:10       ` Zhou, Danny
2014-10-22  7:35         ` alex
2014-10-22  8:53           ` Liang, Cunming
2014-10-22 15:21             ` Zhou, Danny
2014-10-23  7:49               ` Alex Markuze
2014-10-27 17:27               ` Shivapriya Hiremath
2014-10-27 17:32                 ` Zhou, Danny
2014-10-30 23:22                 ` Zhou, Danny
2014-10-31  0:05                   ` Shivapriya Hiremath

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