Messages in this thread | | | Date | Wed, 26 Apr 2017 23:59:36 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH V2] x86/tboot: add an option to disable iommu force on |
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On Wed, Apr 26, 2017 at 09:18:35AM -0700, Shaohua Li wrote: > IOMMU harms performance signficantly when we run very fast networking > workloads. It's 40GB networking doing XDP test. Software overhead is > almost unaware, but it's the IOTLB miss (based on our analysis) which > kills the performance. We observed the same performance issue even with > software passthrough (identity mapping), only the hardware passthrough > survives. The pps with iommu (with software passthrough) is only about > ~30% of that without it. 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. > > So introduce a new boot option to disable the force on. It's kind of > silly we need to run into intel_iommu_init even without force on, but we > need to disable TBOOT PMR registers. For system without the boot option, > nothing is changed. > > Signed-off-by: Shaohua Li <shli@fb.com>
Applied, thanks.
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