linux-kernel - Re: [PATCH 03/23] AMD IOMMU: implement lazy IO/TLB flushing

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Date:	Thu, 18 Sep 2008 12:13:38 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	joro@...tes.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/23] AMD IOMMU: implement lazy IO/TLB flushing

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@...tes.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@....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@....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 introduce a parameter called '[no]fullflush' like the GART already uses.
We can remove this parameter from gart_parse_options() later then.

Joerg

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