[PATCH v4] drm/i915: Use Transparent Hugepages when IOMMU is enabled
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Wed Sep 8 08:44:56 UTC 2021
On 07/09/2021 12:13, Eero Tamminen wrote:
> Hi,
>
> For completeness sake, it might be worth mentioning specifically what
> (synthetic) test-cases regress with THP patch.
>
> * Skylake GT4e:
> 20-25% SynMark TexMem*
> (whereas all MemBW GPU tests either improve or are not affected)
>
> * Broxton J4205:
> 7% MemBW GPU texture
> 2-3% SynMark TexMem*
>
> * Tigerlake-H:
> 7% MemBW GPU blend
Ah right that makes sense. All the entries marker with asterisk under
the "with patch" list. Okay if I just add an explanation on what does
the asterisk mean for them at a single place?
And about the Broxton one. In the bug you put "15-20% MemBW GPU texture"
and "10% SynMark TexMem*" so from where are these numbers now?
>
> I have no idea why on GEN9 texture accesses regress, but on GEN12 TGL
> it's render buffer blend that regresses.
>
> Blend (read+write) regressing is especially odd, as neither render
> buffer read nor write regresses.
>
> Maybe that is a GEN12 specific driver bug similar to Mesa/i965 bug from
> few years back in how its shaders access render buffer, that had caused
> SIMD32 accesses to regress memory BW bound test-cases perf a bit
> compared to SIMD16?
>
> (Blend test is likely to run nowadays as SIMD32.)
No idea on this one from me, leaving to more qualified people to comment.
Regards,
Tvrtko
>
> - Eero
>
> On 7.9.2021 13.34, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>
>> Usage of Transparent Hugepages was disabled in 9987da4b5dcf
>> ("drm/i915: Disable THP until we have a GPU read BW W/A"), but since it
>> appears majority of performance regressions reported with an enabled
>> IOMMU
>> can be almost eliminated by turning them on, lets just do that.
>>
>> To err on the side of safety we keep the current default in cases where
>> IOMMU is not active, and only when it is default to the
>> "huge=within_size"
>> mode. Although there probably would be wins to enable them throughout,
>> more extensive testing across benchmarks and platforms would need to be
>> done.
>>
>> With the patch and IOMMU enabled my local testing on a small Skylake part
>> shows OglVSTangent regression being reduced from ~14% (IOMMU on versus
>> IOMMU off) to ~2% (same comparison but with THP on).
>>
>> More detailed testing done in the below referenced Gitlab issue by Eero:
>>
>> Skylake GT4e:
>>
>> Performance drops from enabling IOMMU:
>>
>> 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 patch drops become:
>>
>> 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
>>
>> Broxton:
>>
>> Performance 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
>>
>> Tigerlake-H:
>>
>> 20-25% MemBW GPU texture
>> 15-20% GpuTest Triangle
>> 13-15% SynMark TerrainFly* + DeferredAA + HdrBloom
>> 8-10% GfxBench Manhattan 3.1, SynMark TerrainPan* + DrvRes
>> 6-7% GfxBench Manhattan 3.0, SynMark TexMem*
>> 4-8% GLB onscreen Fill + T-Rex + Egypt (more in onscreen than
>> offscreen versions of T-Rex/Egypt)
>> 4-6% GfxBench CarChase + GLES AztecRuins + ALU2, GpuTest 32-bit
>> Julia,
>> SynMark CSDof + DrvState
>> 3-5% GfxBench T-Rex + Egypt, Unigine Heaven + Valley, GpuTest Plot3D
>> 1-7% Media tests
>> 2-3% MemBW GPU blit
>> 1-3% Most of the rest of 3D tests
>>
>> With the patch:
>>
>> 6-8% MemBW GPU blend => the only regression in these tests (compared
>> to IOMMU without THP)
>> 4-6% SynMark DrvState (not impacted) + HdrBloom (improved)
>> 3-4% GLB T-Rex
>> ~3% GLB Egypt, SynMark DrvRes
>> 1-3% GfxBench T-Rex + Egypt, SynMark TexFilterTri
>> 1-2% GfxBench CarChase + GLES AztecRuins, Unigine Valley,
>> GpuTest Triangle
>> ~1% GfxBench Manhattan 3.0/3.1, Unigine Heaven
>>
>> Perf of several tests actually improved with IOMMU + THP, compared to no
>> IOMMU / no THP:
>>
>> 10-15% SynMark Batch[0-3]
>> 5-10% MemBW GPU texture, SynMark ShMapVsm
>> 3-4% SynMark Fill* + Geom*
>> 2-3% SynMark TexMem512 + CSCloth
>> 1-2% SynMark TexMem128 + DeferredAA
>>
>> v2:
>> * Add Kconfig dependency to transparent hugepages and some help text.
>> * Move to helper for easier handling of kernel build options.
>>
>> v3:
>> * Drop Kconfig. (Daniel)
>>
>> v4:
>> * Add some benchmark results to commit message.
>>
>> References: b901bb89324a ("drm/i915/gemfs: enable THP")
>> References: 9987da4b5dcf ("drm/i915: Disable THP until we have a GPU
>> read BW W/A")
>> References: https://gitlab.freedesktop.org/drm/intel/-/issues/430
>> Co-developed-by: Chris Wilson <chris at chris-wilson.co.uk>
>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>> Cc: Matthew Auld <matthew.auld at intel.com>
>> Cc: Eero Tamminen <eero.t.tamminen at intel.com>
>> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>> Cc: Daniel Vetter <daniel at ffwll.ch>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com> # v1
>> ---
>> drivers/gpu/drm/i915/gem/i915_gemfs.c | 22 +++++++++++++++++++---
>> 1 file changed, 19 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gemfs.c
>> b/drivers/gpu/drm/i915/gem/i915_gemfs.c
>> index 5e6e8c91ab38..dbdbdc344d87 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
>> @@ -6,7 +6,6 @@
>> #include <linux/fs.h>
>> #include <linux/mount.h>
>> -#include <linux/pagemap.h>
>> #include "i915_drv.h"
>> #include "i915_gemfs.h"
>> @@ -15,6 +14,7 @@ int i915_gemfs_init(struct drm_i915_private *i915)
>> {
>> struct file_system_type *type;
>> struct vfsmount *gemfs;
>> + char *opts;
>> type = get_fs_type("tmpfs");
>> if (!type)
>> @@ -26,10 +26,26 @@ int i915_gemfs_init(struct drm_i915_private *i915)
>> *
>> * One example, although it is probably better with a per-file
>> * control, is selecting huge page allocations
>> ("huge=within_size").
>> - * Currently unused due to bandwidth issues (slow reads) on
>> Broadwell+.
>> + * However, we only do so to offset the overhead of iommu lookups
>> + * due to bandwidth issues (slow reads) on Broadwell+.
>> */
>> - gemfs = kern_mount(type);
>> + opts = NULL;
>> + if (intel_vtd_active()) {
>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
>> + static char huge_opt[] = "huge=within_size"; /* r/w */
>> +
>> + opts = huge_opt;
>> + drm_info(&i915->drm,
>> + "Transparent Hugepage mode '%s'\n",
>> + opts);
>> + } else {
>> + drm_notice(&i915->drm,
>> + "Transparent Hugepage support is recommended for
>> optimal performance when IOMMU is enabled!\n");
>> + }
>> + }
>> +
>> + gemfs = vfs_kern_mount(type, SB_KERNMOUNT, type->name, opts);
>> if (IS_ERR(gemfs))
>> return PTR_ERR(gemfs);
>>
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