On Thu, Sep 09, 2021 at 12:44:48PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> 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
>
> As a summary across all platforms, these are the benchmarks where enabling
> THP on top of IOMMU enabled brings regressions:
>
> * 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
>
> Other benchmarks show either lowering of regressions or improvements.
>
> 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.
>
> v5:
> * Add explicit regression summary to commit message. (Eero)
>
> 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@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Eero Tamminen <eero.t.tamminen@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx> # v1
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> ---
> 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);
>
> --
> 2.30.2
>
