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    SubjectRe: [PATCH 03/23] AMD IOMMU: implement lazy IO/TLB flushing
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    On Thu, 18 Sep 2008 16:03:50 +0200
    Joerg Roedel <joerg.roedel@amd.com> wrote:

    > On Thu, Sep 18, 2008 at 10:29:24AM +0900, FUJITA Tomonori wrote:
    > > On Wed, 17 Sep 2008 21:28:27 +0200
    > > Joerg Roedel <joro@8bytes.org> wrote:
    > >
    > > > 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.
    > >
    > > Hmm, now is better than the future? I think that now you can add
    > > something like 'disable_batching_flush' as a common parameter and
    > > change AMD IOMMU to use it.
    >
    > Ok, I queued the following patch in the AMD IOMMU updates and changed
    > this patch to use iommu_fullflush instead. Is this patch ok? It changes
    > the behavior of GART to use lazy flushing by default. But I don't think
    > that this is a problem.
    >
    > commit 9769771290fddcfc0362c5d30242151d4eb1cc46
    > Author: Joerg Roedel <joerg.roedel@amd.com>
    > Date: Thu Sep 18 15:23:43 2008 +0200
    >
    > x86: move GART TLB flushing options to generic code
    >
    > The GART currently implements the iommu=[no]fullflush command line
    > parameters which influence its IO/TLB flushing strategy. This patch
    > makes these parameters generic so that they can be used by the AMD IOMMU
    > too.
    >
    > Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
    >
    > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    > index c2e00ee..569527e 100644
    > --- a/Documentation/kernel-parameters.txt
    > +++ b/Documentation/kernel-parameters.txt
    > @@ -888,6 +888,10 @@ and is between 256 and 4096 characters. It is defined in the file
    > nomerge
    > forcesac
    > soft
    > + fullflush
    > + Flush IO/TLB at every deallocation
    > + nofullflush
    > + Flush IO/TLB only when addresses are reused (default)

    I'm not sure about making 'nofullflush' a generic option. Enabling
    nofullflush option doesn't change anything. So what's the point of the
    option?


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