linux-kernel - Re: [PATCH V2] x86/tboot: add an option to disable iommu force on

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Date:   Thu, 27 Apr 2017 17:18:55 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Shaohua Li <shli@...com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        gang.wei@...el.com, hpa@...ux.intel.com, kernel-team@...com,
        ning.sun@...el.com, srihan@...com, alex.eydelberg@...el.com
Subject: Re: [PATCH V2] x86/tboot: add an option to disable iommu force on

On Thu, Apr 27, 2017 at 07:49:02AM -0700, Shaohua Li wrote:
> This is exactly the usage for us. And please note, not everybody should
> sacrifice the DMA security. It is only required when the pcie device hits iommu
> hardware limitation. In our enviroment, normal network workloads (as high as
> 60k pps) are completely ok with iommu enabled. Only the XDP workload, which can
> do around 200k pps, is suffering from the problem. So completely forcing iommu
> off for some workloads without the performance issue isn't good because of the
> DMA security.

How big are the packets in your XDP workload? I also run pps tests for
performance measurement on older desktop-class hardware
(Xeon E5-1620 v2 and AMD FX 6100) and 10GBit network
hardware, and easily get over the 200k pps mark with IOMMU enabled. The
Intel system can receive >900k pps and the AMD system is still at
~240k pps.

But my tests only send IPv4/UDP packets with 8bytes of payload, so that
is probably different to your setup.

	Joerg