CONFIG_IOMMU_VMERGE: Enable IOMMU virtual merging

General informations

The Linux kernel configuration item CONFIG_IOMMU_VMERGE has multiple definitions:

Enable IOMMU virtual merging found in arch/powerpc/Kconfig

The configuration item CONFIG_IOMMU_VMERGE:

• prompt: Enable IOMMU virtual merging
• type: bool
• depends on: CONFIG_PPC64
• defined in arch/powerpc/Kconfig
• found in Linux kernels: 2.6.24–2.6.33

Help text

Cause IO segments sent to a device for DMA to be merged virtually by the IOMMU when they happen to have been allocated contiguously. This doesn't add pressure to the IOMMU allocator. However, some drivers don't support getting large merged segments coming back from *_map_sg().

Most drivers don't have this problem; it is safe to say Y here.

Enable IOMMU virtual merging (EXPERIMENTAL) found in arch/powerpc/Kconfig

The configuration item CONFIG_IOMMU_VMERGE:

• prompt: Enable IOMMU virtual merging (EXPERIMENTAL)
• type: bool
• depends on: CONFIG_EXPERIMENTAL && CONFIG_PPC64
• defined in arch/powerpc/Kconfig
• found in Linux kernels: 2.6.15–2.6.23

Help text

Cause IO segments sent to a device for DMA to be merged virtually by the IOMMU when they happen to have been allocated contiguously. This doesn't add pressure to the IOMMU allocator. However, some drivers don't support getting large merged segments coming back from *_map_sg(). Say Y if you know the drivers you are using are properly handling this case.

Enable IOMMU virtual merging (EXPERIMENTAL) found in arch/ppc64/Kconfig

The configuration item CONFIG_IOMMU_VMERGE:

• prompt: Enable IOMMU virtual merging (EXPERIMENTAL)
• type: bool
• depends on: CONFIG_EXPERIMENTAL
• defined in arch/ppc64/Kconfig
• found in Linux kernels: 2.6.4–2.6.14

Help text

Cause IO segments sent to a device for DMA to be merged virtually by the IOMMU when they happen to have been allocated contiguously. This doesn't add pressure to the IOMMU allocator. However, some drivers don't support getting large merged segments coming back from *_map_sg(). Say Y if you know the drivers you are using are properly handling this case.

Hardware

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The data is retrived from:

• Linux kernel
• Linux Kernel Driver DataBase (LKDDb)

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