Messages in this thread | | | Date | Wed, 17 Sep 2008 21:28:27 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH 03/23] AMD IOMMU: implement lazy IO/TLB flushing |
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On Thu, Sep 18, 2008 at 04:20:18AM +0900, FUJITA Tomonori wrote: > 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?
True. We should merge common parameters across IOMMUs into the iommu= parameter some time in the future, I think. It would also be the place for the IOMMU size parameter.
> 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.
This is exactly what AMD IOMMU with this patch does too. The amd_iommu=unmap_flush parameter disables lazy IO/TLB flushing.
Joerg
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