linux-kernel - Re: [RFC] x86/tboot: add an option to disable iommu force on

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Date:   Wed, 22 Mar 2017 11:49:00 +0100
From:   Joerg Roedel <jroedel@...e.de>
To:     Shaohua Li <shli@...com>
Cc:     linux-kernel@...r.kernel.org, gang.wei@...el.com,
        hpa@...ux.intel.com, mingo@...nel.org, kernel-team@...com,
        ning.sun@...el.com, srihan@...com, alex.eydelberg@...el.com
Subject: Re: [RFC] x86/tboot: add an option to disable iommu force on

Hi Shaohua,

On Tue, Mar 21, 2017 at 11:37:51AM -0700, Shaohua Li wrote:
> IOMMU harms performance signficantly when we run very fast networking
> workloads. This is a limitation in hardware based on our observation, so
> we'd like to disable the IOMMU force on, but we do want to use TBOOT and
> we can sacrifice the DMA security bought by IOMMU. I must admit I know
> nothing about TBOOT, but TBOOT guys (cc-ed) think not eabling IOMMU is
> totally ok.

Can you elaborate a bit more on the setup where the IOMMU still harms
network performance? With the recent scalability improvements I measured
only a minimal impact on 10GBit networking.



	Joerg