[GEN9+] large perf drop (up to 1/3) in most 3D benchmarks from force-enabling IOMMU

added Community feature: Perf/PMU platform: BXT platform: ICL platform: KBL platform: SKL priority::high severity::major + 1 deleted label

Chris Wilson @ickle said:

drm/i915: Make i915_vma.flags atomic_t for mutex reduction
drm/i915: Make shrink/unshrink be atomic

are meh.

drm/i915: Whitelist COMMON_SLICE_CHICKEN2

is a possiblity, but my money is on

drm/i915: Force compilation with intel-iommu for CI validation

A run with intel_iommu=off should test that theory, or intel_iommu=igfx_off and reverting HAX iommu/intel: Ignore igfx_off

Eero Tamminen @eero-t said:

(In reply to Chris Wilson from comment 1)

drm/i915: Make i915_vma.flags atomic_t for mutex reduction
drm/i915: Make shrink/unshrink be atomic

are meh.

drm/i915: Whitelist COMMON_SLICE_CHICKEN2

is a possiblity, but my money is on

drm/i915: Force compilation with intel-iommu for CI validation

A run with intel_iommu=off should test that theory, or intel_iommu=igfx_off
and reverting HAX iommu/intel: Ignore igfx_off

We run all tests currently with "intel_iommu=igfx_off" kernel command line option, and while the author-date in above intel-iommu/igfx_off commits is within range, their drm-tip repo commit dates are actually from Monday this week, not from week ago?

(Why IOMMU perf impact would be SKL GT4e specific?)

Also, whereas latest drm-tip kernel shows:
$ sudo grep mmu /sys/kernel/debug/dri/0/i915_capabilities
iommu: enabled

There's no such output for the 2019-09-11 "b27acd37b7de" kernel where this regression was noticed.

There is a difference on kernel IOMMU outputs between these commits though...

Before:
[ 0.625811] DMAR: No ATSR found
[ 0.625842] DMAR: dmar1: Using Queued invalidation
[ 0.625948] pci 0000:00:00.0: Adding to iommu group 0
[ 0.625993] pci 0000:00:08.0: Adding to iommu group 1
[ 0.626054] pci 0000:00:14.0: Adding to iommu group 2
[ 0.626064] pci 0000:00:14.2: Adding to iommu group 2
[ 0.626110] pci 0000:00:16.0: Adding to iommu group 3
[ 0.626159] pci 0000:00:1c.0: Adding to iommu group 4
[ 0.626203] pci 0000:00:1c.1: Adding to iommu group 5
[ 0.626249] pci 0000:00:1c.4: Adding to iommu group 6
[ 0.626296] pci 0000:00:1d.0: Adding to iommu group 7
[ 0.626348] pci 0000:00:1f.0: Adding to iommu group 8
[ 0.626359] pci 0000:00:1f.2: Adding to iommu group 8
[ 0.626368] pci 0000:00:1f.3: Adding to iommu group 8
[ 0.626378] pci 0000:00:1f.4: Adding to iommu group 8
[ 0.626422] pci 0000:00:1f.6: Adding to iommu group 9
[ 0.626467] pci 0000:02:00.0: Adding to iommu group 10
[ 0.626518] pci 0000:3c:00.0: Adding to iommu group 11
[ 0.626523] DMAR: Intel(R) Virtualization Technology for Directed I/O

After:
[ 0.625808] DMAR: No ATSR found
[ 0.625837] DMAR: dmar0: Using Queued invalidation
[ 0.625841] DMAR: dmar1: Using Queued invalidation
[ 0.626033] pci 0000:00:00.0: Adding to iommu group 0
[ 0.632522] pci 0000:00:02.0: Adding to iommu group 1
[ 0.632568] pci 0000:00:08.0: Adding to iommu group 2
[ 0.632634] pci 0000:00:14.0: Adding to iommu group 3
[ 0.632644] pci 0000:00:14.2: Adding to iommu group 3
[ 0.632684] pci 0000:00:16.0: Adding to iommu group 4
[ 0.632746] pci 0000:00:1c.0: Adding to iommu group 5
[ 0.632797] pci 0000:00:1c.1: Adding to iommu group 6
[ 0.632854] pci 0000:00:1c.4: Adding to iommu group 7
[ 0.632911] pci 0000:00:1d.0: Adding to iommu group 8
[ 0.632966] pci 0000:00:1f.0: Adding to iommu group 9
[ 0.632977] pci 0000:00:1f.2: Adding to iommu group 9
[ 0.632988] pci 0000:00:1f.3: Adding to iommu group 9
[ 0.632998] pci 0000:00:1f.4: Adding to iommu group 9
[ 0.633039] pci 0000:00:1f.6: Adding to iommu group 10
[ 0.633096] pci 0000:02:00.0: Adding to iommu group 11
[ 0.633146] pci 0000:3c:00.0: Adding to iommu group 12
[ 0.633233] DMAR: Intel(R) Virtualization Technology for Directed I/O

Other IOMMU / DMAR related dmesg output is identical between the commits:
[ 0.002741] ACPI: DMAR 0x000000007A545CD8 0000A8 (v01 INTEL NUC6i7KY 00000001 INTL 00000001)
...
[ 0.125612] Kernel command line: BOOT_IMAGE=/boot/drm_intel root=/dev/nvme0n1p2 rootwait fsck.repair=yes intel_iommu=igfx_off ro
...
[ 0.174960] DMAR: Host address width 39
[ 0.174962] DMAR: DRHD base: 0x000000fed90000 flags: 0x0
[ 0.174967] DMAR: dmar0: reg_base_addr fed90000 ver 1:0 cap 1c0000c40660462 ecap 7e3ff0505e
[ 0.174970] DMAR: DRHD base: 0x000000fed91000 flags: 0x1
[ 0.174975] DMAR: dmar1: reg_base_addr fed91000 ver 1:0 cap d2008c40660462 ecap f050da
[ 0.174978] DMAR: RMRR base: 0x0000007a275000 end: 0x0000007a294fff
[ 0.174980] DMAR: RMRR base: 0x0000007b800000 end: 0x0000007fffffff
[ 0.174983] DMAR-IR: IOAPIC id 2 under DRHD base 0xfed91000 IOMMU 1
[ 0.174985] DMAR-IR: HPET id 0 under DRHD base 0xfed91000
[ 0.174987] DMAR-IR: Queued invalidation will be enabled to support x2apic and Intr-remapping.
[ 0.176506] DMAR-IR: Enabled IRQ remapping in x2apic mode

PS. This regression is large enough that one run of CSDof is enough to see whether kernel version is impacted:
./synmark2 OglCSDof

Chris Wilson @ickle said:

(In reply to Eero Tamminen from comment 2)

(In reply to Chris Wilson from comment 1)

drm/i915: Make i915_vma.flags atomic_t for mutex reduction
drm/i915: Make shrink/unshrink be atomic

are meh.

drm/i915: Whitelist COMMON_SLICE_CHICKEN2

is a possiblity, but my money is on

drm/i915: Force compilation with intel-iommu for CI validation

A run with intel_iommu=off should test that theory, or intel_iommu=igfx_off
and reverting HAX iommu/intel: Ignore igfx_off

We run all tests currently with "intel_iommu=igfx_off" kernel command line
option, and while the author-date in above intel-iommu/igfx_off commits is
within range, their drm-tip repo commit dates are actually from Monday this
week, not from week ago?

The commit is in core-for-CI which is a rebasing tree; on Monday it was rebased to v5.3 so that we could drop some patches. So the commit id will be updated fairly often while it remains in that branch.

> (Why IOMMU perf impact would be SKL GT4e specific?)

My guess at this moment would be that eDRAM feels the hit more significantly. Or that we've just got the caching completely wrong on that sku.

> Also, whereas latest drm-tip kernel shows:
> $ sudo grep mmu /sys/kernel/debug/dri/0/i915_capabilities
> iommu: enabled
>
> There's no such output for the 2019-09-11 "b27acd37b7de" kernel where this
> regression was noticed.

That is a new feature added so that we could easily determine which machines in the farm have iommu enabled.

> There is a difference on kernel IOMMU outputs between these commits though...
>
[snip]
> After:
> [ 0.632522] pci 0000:00:02.0: Adding to iommu group 1

So we definitely enabled iommu on igfx in this range.

> PS. This regression is large enough that one run of CSDof is enough to see
> whether kernel version is impacted:
> ./synmark2 OglCSDof

20+% regression is also in line with some kbl (gt3e iirc) media runs I did.

Eero Tamminen @eero-t said:

(In reply to Chris Wilson from comment 3)

(Why IOMMU perf impact would be SKL GT4e specific?)

My guess at this moment would be that eDRAM feels the hit more
significantly. Or that we've just got the caching completely wrong on that
sku.

We were supposed to have VT-d disabled from BIOS in all our machines, but apparently that had been enabled when SkullCanyon was in other use for a while. I.e. it was only machine with VT-d enabled.

> 20+% regression is also in line with some kbl (gt3e iirc) media runs I did.

Media, not 3D? (That's more than I saw on SkullCanyon in media test-cases.)

I've now enabled VT-d on few other machines (BDW GT2, BXT, SKL GT2, KBL GT3e) to get you a bit more perf info. I'll add that info here later this week.

Jon Ewins uploaded an attachment:

I am currently away and will respond when I return

Attachment 145433, "attachment-21608-0.html":
attachment-21608-0.html

Eero Tamminen @eero-t said:

Largest performance drops from IOMMU with recent user-space 3D / Media stack are following (all machines have dual channel memory)...

SKL GT4e (i7-6770HQ)
--------------------

25-30% SynMark CSDof (fullscreen)
20-25% GpuTest windowed 1/2 screen Triangle, SynMark VSTangent
20-25% SynMark Fill* [1]
20% Unigine Heaven
20% GpuTest fullscreen Triangle, SynMark DeferredAA [2]
10-20% GLB 2.7 windowed 1/2 screen Egypt & T-Rex
10-20% SynMark ZBuffer & Deferred [2]
10-15% SynMark TexMem512, GPU write [1]
5-10% GfxBench T-Rex, Manhattan 3.0 & 3.1, CarChase, SynMark TerrainFly*

5% Unigine Valley, GfxBench AztecRuins<br>

2-3% 8-bit, max FullHD, FFmpeg/MediaSDK GPU transcode/downscale

[1] With June user-space. With latest Mesa, Fill* & write tests drop is only 3%, and TexMem512 perf somehow improves by 2%. Latest Mesa is several percent faster than older one in these tests, due to Mesa slice/subslice balance optimization, no idea how that can reduce impact of IOMMU.

[2] With June user-space. With latest user-space, drop in these specific tests is half of that, or less. For fullscreen Triangle case, potentially relevant user-space change could be latest X server disabling atomic commits. See: xorg/xserver#888 (closed)

KBL GT3e (i7-7567U)
-------------------

* 30-35% SynMark Fill* [1]
* 20-25% GpuTest windowed 1/2 screen Triangle, SynMark VSTangent
* 10-15% GLB 2.7 windowed 1/2 screen Egypt & T-Rex, SynMark ZBuffer
* 10-15% GpuTest fullscreen Triangle, GPU write [1]
* 10-15% 4K HEVC GPU decode + hwdownload
* 5-10% Unigine Heaven, GfxBench T-Rex, Manhattan 3.0 & 3.1 & CarChase, SynMark CSDof
* 5-10% SynMark Deferred* [1]
* 5-10% 10-bit, 4K HEVC GPU transcode
* 2-3% 8-bit, max FullHD, FFmpeg/MediaSDK GPU transcode/downscale

[1] With June user-space. With latest user-space, drop in these specific tests is about half.

SKL GT2 (i5-6600K)
------------------

* >25% GPU write, SynMark VSTangent
* 20% SynMark Fill*, GpuTest windowed Triangle
* 15-20% GLB Egypt
* 15% SynMark ZBuffer
* 10% GLB T-Rex, GpuTest fullscreen Triangle
* 5-10% GfxBench Manhattan 3.0 & 3.1, T-Rex, CarChase
* 5% GfxBench AztecRuins, Unigine Heaven
* 2-6% 8-bit, max FullHD, FFmpeg/MediaSDK GPU transcode/downscale

With the June user-space, there are some differences in how much performance drops, but nothing major like with GT3e & GT4e (where slice/subslice issue balance had noticeable impact).

BXT J4205
---------

Results similar to other devices (not reported here as this has higher variances than them). Similarly to SKL GT2, user-space version doesn't have significant impact on how much IOMMU regresses performance.

BDW GT2
-------

As expected, no impact (kernel skips IOMMU for BDW).

Summary
-------

* IOMMU can lose up to third of performance in worst synthetic case, and 5-15% in real GPU (3d/Media) use-cases.

* Seems that badly balanced sub/slice utilization could have noticeable impact in IOMMU performance impact for some use-cases.

Eero Tamminen @eero-t said:

ICL-U with IOMMU
----------------

Performance didn't improve in any test from enabling IOMMU. Largest performance drops are following:

30% SynMark VSTangent & ZBuffer
24% MemBW GPU write (with i965, 6-7% with Iris & higher FPS (*))
18% GLB 2.7 Egypt (windowed), SynMark VSDiffuse*
17% GpuTest v0.7 Triangle (windowed)
15% MemBW GPU blit (with i965, 20% with Iris & lower FPS (*))
14% GLB 2.7 T-Rex (windowed), SynMark HdrBloom
5-15% HEVC decode & download
11-12% GfxBench Manhattan 3.0 & 31, GpuTest Triangle, SynMark DrvRes
9-11% GfxBench T-Rex & CarChase, SynMark TerrainFly*
7-9% GfxBench AztecRuins, SynMark TexMem128, DeferredAA, ShMapVsm
5-7% Unigine Heaven & Valley, GfxBench ALU2, SynMark TexMem512, Deferred, TerrainPan*, CSCloth
2-6% 8-bit <FullHD Media transcode

(*) Iris doesn't support E2E RBC, so in onscreen tests it uses more bandwidth / frame, and therefore has lower perf.

PS. 30% perf drop from enabling IOMMU == >40% perf increase from disabling IOMMU.

added feature: IOMMU label and removed feature: Perf/PMU label

Hi @bugzilla-migration @eero-t , please confirm if this issue is still seen on latest kernel also.

If yes, provide the steps to reproduce it for further debugging.

@ysainan I haven't seen any indication that situation would have improved (and I assume part of it is HW related). If you can provide some, I can do testing.

can you try to reproduce this issue on latest drm-tip.

https://cgit.freedesktop.org/drm-tip

Please post your observations on it and any steps followed to reproduce the issue.

@ysainan, why you keep pinging this, is there some reason why the situation would have changed?

I don't have any newer HW to test whether they would have HW mitigations to lower performance impact of IOMMU.

I would suggest somebody from kernel team to test this with single use-case and if there's some actual improvement visible, I can do testing with full set of benchmarks and more HW.

It is likely this is almost purely related to TLB (the IOMMU one) trashing and can be improved dramatically by using transparent huge pages. i915 patch to re-enable them is quite simple, but I sadly don't have access to any automated performance testing suite. All I can say is I tested locally on a low power Skylake GT2 part and for instance regression on OglVSTangent goes from ~14% to 2-3%.

There is a possibility things could be further improved on some benchmarks by triggering less DMA unmap (hence TLB flushes) from i915 but at least for the above benchmark that wasn't the case.

Patch to test with, if someone has the capability (@eero-t ? ;)), looks like this:

diff --git a/drivers/gpu/drm/i915/gem/i915_gemfs.c b/drivers/gpu/drm/i915/gem/i915_gemfs.c
index 5e6e8c91ab38..afbea13b6cd0 100644
--- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
+++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
@@ -15,6 +15,7 @@ int i915_gemfs_init(struct drm_i915_private *i915)
 {
        struct file_system_type *type;
        struct vfsmount *gemfs;
+       char opts[] = "huge=within_size";
 
        type = get_fs_type("tmpfs");
        if (!type)
@@ -29,7 +30,7 @@ int i915_gemfs_init(struct drm_i915_private *i915)
         * Currently unused due to bandwidth issues (slow reads) on Broadwell+.
         */
 
-       gemfs = kern_mount(type);
+       gemfs = vfs_kern_mount(type, SB_KERNMOUNT, type->name, opts);
        if (IS_ERR(gemfs))
                return PTR_ERR(gemfs);

P.S. In case THP turns out to be a big win for intel_iommu=on, it would be very handy to have results with and without this patch, with IOMMU off as well. Because I am told there was a performance issue on some platforms which was the reason we turned off THP.

Patch to test with, if someone has the capability (@eero-t ? ;))

@tursulin If you provide the change as separate patch or commit, I could do some more testing for it.

Currently my test setup has only GEN9 machines and one TGL (GT1) device. I have no discrete GPUs, but I should be able to loan a DG1 for few days.

I would start by doing testing with full 3D benchmark set on SkullCanyon (SKL GT4e) as that large CSDof (3d compute) case drop on it was especially interesting. Large drops in GPU (onscreen) writes with IOMMU would be next thing to check as it happened for all devices.

@eero-t does https://patchwork.freedesktop.org/patch/447734/?series=93182&rev=1 work for you?

Also, I assume DG1 is not very interesting since IOMMU would be involved much less in any bandwidth intensive operations given the data set is supposed to me in device local memory. But Gen9 and TGL would definitely be interesting.

Patch built fine. GEN9 & TGL are better as those I can access right away.

All devices I'm testing have VT-d disabled from BIOS, so I guess I need to ask somebody at the office to enable that for the test devices (earlier devices had "intel_iommu=igfx_off" to avoid the slowdown / instability, but that does not seem to be used now that all have VT-d disabled in BIOS).

Is there anything else that needs to be changed / enabled in BIOS transparent hugepages? What about kernel command line?

And are these options enough in kernel config?

$ grep -e IOMMU -e HUGE
kconfig/default:# CONFIG_GART_IOMMU is not set
kconfig/default:# CONFIG_CALGARY_IOMMU is not set
kconfig/default:CONFIG_IOMMU_API=y
kconfig/default:CONFIG_IOMMU_SUPPORT=y
kconfig/default:# Generic IOMMU Pagetable Support
kconfig/default:# CONFIG_IOMMU_DEBUGFS is not set
kconfig/default:# CONFIG_IOMMU_DEFAULT_PASSTHROUGH is not set
kconfig/default:CONFIG_IOMMU_IOVA=y
kconfig/default:# CONFIG_AMD_IOMMU is not set
kconfig/default:CONFIG_INTEL_IOMMU=y
kconfig/default:# CONFIG_INTEL_IOMMU_SVM is not set
kconfig/default:CONFIG_INTEL_IOMMU_DEFAULT_ON=y
kconfig/default:CONFIG_INTEL_IOMMU_FLOPPY_WA=y
...
CONFIG_CGROUP_HUGETLB=y
CONFIG_ARCH_WANT_HUGE_PMD_SHARE=y
CONFIG_ARCH_WANT_GENERAL_HUGETLB=y
CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION=y
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD=y
CONFIG_HAVE_ARCH_HUGE_VMAP=y
CONFIG_TRANSPARENT_HUGEPAGE=y
CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
# CONFIG_TRANSPARENT_HUGEPAGE_MADVISE is not set
CONFIG_TRANSPARENT_HUGE_PAGECACHE=y
CONFIG_HUGETLBFS=y
CONFIG_HUGETLB_PAGE=y

What I should see in dmesg when everything is working as expected?

Looks okay.

For the hugepages side of things in dmesg you should see "Transparent Hugepage mode 'huge=within_size'" and absence of "Unable to create a private tmpfs mount, hugepage support will be disabled". Both come from i915.

And for the IOMMU side "i915 device info: iommu: enabled". (There's a bunch of other dmesg lines containing either iommu or dmar which appear when thing is active but that one should be sufficient indicator.)

Correct message to check for was: "[drm] VT-d active for gfx access".

Performance drops from enabling "VT-d" & "Intel Virtualization Technology" & "intel_iommu=on" are following on SkullCanyon (SKL GT4e) with current drm-tip:

30-35% SynMark CSDof
20-25% Unigine Heaven, MemBW GPU write, SynMark VSTangent
~20% GLB Egypt (1/2 screen window)
10-15% GLB T-Rex (1/2 screen window)
8-10% GfxBench T-Rex, MemBW GPU blit
7-8% SynMark DeferredAA + TerrainFly* + ZBuffer
6-7% GfxBench Manhattan 3.0 + 3.1, SynMark TexMem128 & CSCloth
5-6% GfxBench CarChase, Unigine Valley
3-5% GfxBench Vulkan & GL AztecRuins + ALU2, MemBW GPU texture, SynMark Fill*, Deferred, TerrainPan*
1-2% Most of the other tests

With the THB patch they are:

20-25% SynMark TexMem*
15-20% GLB Egypt (1/2 screen window)
10-15% GLB T-Rex (1/2 screen window)
4-7% GfxBench T-Rex, GpuTest Triangle
1-8% GfxBench ALU2 (offscreen 1%, onscreen 8%)
3% GfxBench Manhattan 3.0, SynMark CSDof
2-3% Unigine Heaven + Valley, MemBW GPU texture
1-3 GfxBench Manhattan 3.1 + CarChase + Vulkan & GL AztecRuins

(Impacts are rough estimates because tests were not run in same order, and each test was run only 3-5 times. I'm listing only tests which results are known to be somewhat stable though.)

Summary so far:

THB (patch) significantly helps most of the tests regressing with GFX IOMMU
There are still significant perf gaps compared to not using IOMMU
THB regresses SynMark TexMem* tests perf hugely (20-25%) [1]
That regression might explain some of the remaining gaps, e.g. why THB did not decrease GLB Egypt/T-Rex IOMMU perf gap at all

[1] This is a known, old hugepages issue. Assumption was that use of hugepages somehow interferes with GPU cache coloring, and as result, workloads which are bandwidth bound (especially ones that quite not fit into cache), can suffer from it.

Tomorrow I'll check whether removing "intel_iommu=on" has any impact on SkullCanyon perf, and check how much Unigine demos regress without the patch. I guess I also need to check whether GEN12 (TGL) also suffers from the same hugepages regression...

EDIT: added Valley/Heaven/AztecRuins perf impact, and moved BXT info to next comment with other BXT data.

As expected, there was no significant perf impact on SkullCanyon from removing "intel_iommu=on".

BXT perf drops from IOMMU, without patch:

30% MemBW GPU write
25% SynMark ZBuffer + Fill*
20% MemBW GPU blit
15% MemBW GPU blend, GpuTest Triangle
10-15% MemBW GPU texture
10% GLB Egypt, Unigine Heaven (had hangs), SynMark TerrainFly*
7-9% GLB T-Rex, GfxBench Manhattan 3.0 + T-Rex, SynMark Deferred* + TexMem*
6-8% GfxBench CarChase, Unigine Valley, SynMark CSCloth + ShMapVsm + TerrainPan*
5-6% GfxBench Manhattan 3.1 + GL AztecRuins, SynMark CSDof + TexFilterTri
2-4% GfxBench ALU2, SynMark DrvRes + GSCloth + ShMapPcf + Batch[0-5] + TexFilterAniso, GpuTest GiMark + 32-bit Julia

And with patch:

15-20% MemBW GPU texture
10% SynMark TexMem*
8-9% GLB Egypt (1/2 screen window)
4-5% GLB T-Rex (1/2 screen window)
3-6% GfxBench Manhattan 3.0, GpuTest FurMark, SynMark Deferred + TexFilterTri
3-4% GfxBench Manhattan 3.1 + T-Rex, SynMark VSInstancing
2-4% GpuTest Triangle, SynMark DeferredAA
2-3% Unigine Heaven + Valley
1-3% SynMark Terrain*
1-2% GfxBench CarChase, SynMark TexFilterAniso + ZBuffer

Summary:

THB patch is a large improvement to IOMMU, but there's still clear gap to non-IOMMU perf
Additional perf regressions with THB are in MemBW GPU texture (7%) and SynMark TexMem* (2-3%) tests

Note: above changes include 2 days of gfxstack updates. Typically there are 0 perf changes, but one never knows. Results correspond to SkullCanyon results though, and as expected regressions from hugepages are much smaller on Atoms (which miss LLC & eDRAM caches, and rest of their caches are much smaller).

[GEN9+] large perf drop (up to 1/3) in most 3D benchmarks from force-enabling IOMMU

Submitted by Eero Tamminen `@eero-t`

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[GEN9+] large perf drop (up to 1/3) in most 3D benchmarks from force-enabling IOMMU

Submitted by Eero Tamminen @eero-t

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