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

From: Joerg Roedel
Date: Thu Sep 18 2008 - 10:04:25 EST

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@xxxxxxxxxx> 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@xxxxxxx> 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@xxxxxxx>
> > > > ---
> > > > 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@xxxxxxx>
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@xxxxxxx>

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)


intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
index 72ffb53..42c887b 100644
--- a/Documentation/x86/x86_64/boot-options.txt
+++ b/Documentation/x86/x86_64/boot-options.txt
@@ -229,8 +229,6 @@ IOMMU (input/output memory management unit)
iommu options only relevant to the AMD GART hardware IOMMU:
<size> Set the size of the remapping area in bytes.
allowed Overwrite iommu off workarounds for specific chipsets.
- fullflush Flush IOMMU on each allocation (default).
- nofullflush Don't use IOMMU fullflush.
leak Turn on simple iommu leak tracing (only when
CONFIG_IOMMU_LEAK is on). Default number of leak pages
is 20.
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 23882c4..6dae123 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -16,6 +16,15 @@ EXPORT_SYMBOL(dma_ops);

static int iommu_sac_force __read_mostly;

+/*
+ * If this is disabled the IOMMU will use an optimized flushing strategy
+ * of only flushing when an mapping is reused. With it true the GART is
+ * flushed for every mapping. Problem is that doing the lazy flush seems
+ * to trigger bugs with some popular PCI cards, in particular 3ware (but
+ * has been also also seen with Qlogic at least).
+ */
+int iommu_fullflush;
+
#ifdef CONFIG_IOMMU_DEBUG
int panic_on_overflow __read_mostly = 1;
int force_iommu __read_mostly = 1;
@@ -171,6 +180,10 @@ static __init int iommu_setup(char *p)
}
if (!strncmp(p, "nomerge", 7))
iommu_merge = 0;
+ if (!strncmp(p, "fullflush", 8))
+ iommu_fullflush = 1;
+ if (!strncmp(p, "nofullflush", 11))
+ iommu_fullflush = 0;
if (!strncmp(p, "forcesac", 8))
iommu_sac_force = 1;
if (!strncmp(p, "allowdac", 8))
diff --git a/arch/x86/kernel/pci-gart_64.c b/arch/x86/kernel/pci-gart_64.c
index 9739d56..508ef47 100644
--- a/arch/x86/kernel/pci-gart_64.c
+++ b/arch/x86/kernel/pci-gart_64.c
@@ -45,15 +45,6 @@ static unsigned long iommu_pages; /* .. and in pages */

static u32 *iommu_gatt_base; /* Remapping table */

-/*
- * If this is disabled the IOMMU will use an optimized flushing strategy
- * of only flushing when an mapping is reused. With it true the GART is
- * flushed for every mapping. Problem is that doing the lazy flush seems
- * to trigger bugs with some popular PCI cards, in particular 3ware (but
- * has been also also seen with Qlogic at least).
- */
-int iommu_fullflush = 1;
-
/* Allocation bitmap for the remapping area: */
static DEFINE_SPINLOCK(iommu_bitmap_lock);
/* Guarded by iommu_bitmap_lock: */
@@ -901,10 +892,6 @@ void __init gart_parse_options(char *p)
#endif
if (isdigit(*p) && get_option(&p, &arg))
iommu_size = arg;
- if (!strncmp(p, "fullflush", 8))
- iommu_fullflush = 1;
- if (!strncmp(p, "nofullflush", 11))
- iommu_fullflush = 0;
if (!strncmp(p, "noagp", 5))
no_agp = 1;
if (!strncmp(p, "noaperture", 10))
diff --git a/include/asm-x86/iommu.h b/include/asm-x86/iommu.h
index 546ad31..bcebc37 100644
--- a/include/asm-x86/iommu.h
+++ b/include/asm-x86/iommu.h
@@ -7,6 +7,7 @@ extern struct dma_mapping_ops nommu_dma_ops;
extern int force_iommu, no_iommu;
extern int iommu_detected;
extern int dmar_disabled;
+extern int iommu_fullflush;

extern unsigned long iommu_num_pages(unsigned long addr, unsigned long len);


--
| AMD Saxony Limited Liability Company & Co. KG
Operating | Wilschdorfer Landstr. 101, 01109 Dresden, Germany
System | Register Court Dresden: HRA 4896
Research | General Partner authorized to represent:
Center | AMD Saxony LLC (Wilmington, Delaware, US)
| General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/