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SubjectRe: [PATCH 03/23] AMD IOMMU: implement lazy IO/TLB flushing
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On Wed, 17 Sep 2008 18:52:37 +0200
Joerg Roedel <joerg.roedel@amd.com> wrote:

> The IO/TLB flushing on every unmaping operation is the most expensive
> part there and not strictly necessary. It is sufficient to do the flush
> before any entries are reused. This is patch implements lazy IO/TLB
> flushing which does exactly this.
>
> Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
> ---
> Documentation/kernel-parameters.txt | 5 +++++
> arch/x86/kernel/amd_iommu.c | 26 ++++++++++++++++++++++----
> arch/x86/kernel/amd_iommu_init.c | 10 +++++++++-
> include/asm-x86/amd_iommu_types.h | 9 +++++++++
> 4 files changed, 45 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index c2e00ee..5f0aefe 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -284,6 +284,11 @@ and is between 256 and 4096 characters. It is defined in the file
> isolate - enable device isolation (each device, as far
> as possible, will get its own protection
> domain)
> + unmap_flush - enable flushing of IO/TLB entries when
> + they are unmapped. Otherwise they are
> + flushed before they will be reused, which
> + is a lot of faster
> +

Would it be nice to have consistency of IOMMU parameters?

VT-d also has the kernel-boot option for this lazy flushing trick
though VT-d 'strict' option is more vague than 'unmap_flush'

It would be also nice to have consistency of IOMMU behavior.

VT-d enables the lazy flushing trick by default and has the boot
option to disable it.


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