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

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Message-Id: <20080918041104K.fujita.tomonori@lab.ntt.co.jp>
Date:	Thu, 18 Sep 2008 04:20:18 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	joerg.roedel@....com
Cc:	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 03/23] AMD IOMMU: implement lazy IO/TLB flushing

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?

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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