From a4c6084830b7f5e32fae9f080683e041f48834cc Mon Sep 17 00:00:00 2001 From: Dominik Csapak Date: Fri, 20 May 2022 10:43:25 +0200 Subject: [PATCH] pcie-passthrough: add short note about iommu passthrough mode that explains in one sentence what it does, that it can increase performance and how to activate it. Signed-off-by: Dominik Csapak --- qm-pci-passthrough.adoc | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/qm-pci-passthrough.adoc b/qm-pci-passthrough.adoc index 5ef325d..28bb4fc 100644 --- a/qm-pci-passthrough.adoc +++ b/qm-pci-passthrough.adoc @@ -62,6 +62,24 @@ The command line parameters are: ---- * for AMD CPUs it should be enabled automatically. + +If your hardware supports it, enabling IOMMU passthrough mode might increase +performance, because then the VMs bypass the (default) DMA translation +which is normally done by the hypervisor, before handing DMA requests off to +the hardware IOMMU. You can enable it with adding + +---- + iommu.passthrough=1 +---- + +or + +---- + iommu=pt +---- + +to the kernel commandline. + .Kernel Modules You have to make sure the following modules are loaded. This can be achieved by -- 2.39.2