On Wed, Jul 28, 2021 at 03:12:49PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursu...@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 do that by adding a
> couple of Kconfig options.
>
> 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% to ~2%.
>
> 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 <ch...@chris-wilson.co.uk>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
> Cc: Matthew Auld <matthew.a...@intel.com>
> Cc: Eero Tamminen <eero.t.tammi...@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
> ---
> drivers/gpu/drm/i915/Kconfig.profile | 46 +++++++++++++++++++++++++++
> drivers/gpu/drm/i915/gem/i915_gemfs.c | 11 +++++--
> 2 files changed, 55 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/Kconfig.profile
> b/drivers/gpu/drm/i915/Kconfig.profile
> index 39328567c200..c64c3d39a0f9 100644
> --- a/drivers/gpu/drm/i915/Kconfig.profile
> +++ b/drivers/gpu/drm/i915/Kconfig.profile
> @@ -119,3 +119,49 @@ config DRM_I915_TIMESLICE_DURATION
> /sys/class/drm/card?/engine/*/timeslice_duration_ms
>
> May be 0 to disable timeslicing.
> +
> +choice
> + prompt "Transparent Hugepage Support (native)"
> + default DRM_I915_THP_NATIVE_NEVER
> + help
> + Select the preferred method for allocating from Transparent Hugepages
> + when IOMMU is not enabled.
> +
> + config DRM_I915_THP_NATIVE_NEVER
> + bool "Never"
> +
> + config DRM_I915_THP_NATIVE_WITHIN
> + bool "Within"
> +
> + config DRM_I915_THP_NATIVE_ALWAYS
> + bool "Always"
> +endchoice
> +
> +config DRM_I915_THP_NATIVE
> + string
> + default "always" if DRM_I915_THP_NATIVE_ALWAYS
> + default "within_size" if DRM_I915_THP_NATIVE_WITHIN
> + default "never" if DRM_I915_THP_NATIVE_NEVER
> +
> +choice
> + prompt "Transparent Hugepage Support (IOMMU)"
> + default DRM_I915_THP_IOMMU_WITHIN
> + help
> + Select the preferred method for allocating from Transparent Hugepages
> + with IOMMU active.
> +
> + config DRM_I915_THP_IOMMU_NEVER
> + bool "Never"
> +
> + config DRM_I915_THP_IOMMU_WITHIN
> + bool "Within"
> +
> + config DRM_I915_THP_IOMMU_ALWAYS
> + bool "Always"
> +endchoice
> +
> +config DRM_I915_THP_IOMMU
> + string
> + default "always" if DRM_I915_THP_IOMMU_ALWAYS
> + default "within_size" if DRM_I915_THP_IOMMU_WITHIN
> + default "never" if DRM_I915_THP_IOMMU_NEVER
> diff --git a/drivers/gpu/drm/i915/gem/i915_gemfs.c
> b/drivers/gpu/drm/i915/gem/i915_gemfs.c
> index 5e6e8c91ab38..b71d2b2d2ada 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
> @@ -13,8 +13,11 @@
>
> int i915_gemfs_init(struct drm_i915_private *i915)
> {
> + char thp_native[] = "huge=" CONFIG_DRM_I915_THP_NATIVE;
> + char thp_iommu[] = "huge=" CONFIG_DRM_I915_THP_IOMMU;
> struct file_system_type *type;
> struct vfsmount *gemfs;
> + char *opts;
>
> type = get_fs_type("tmpfs");
> if (!type)
> @@ -26,15 +29,19 @@ 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+.
> */
> + opts = intel_vtd_active() ? thp_iommu : thp_native;
at first sight I got confused on why we where having to configs, then
very few drivers using the mount option there, so it took me a few
minutes to realize it... but I know understood the goal...
Reviewed-by: Rodrigo Vivi <rodrigo.v...@intel.com>
>
> - gemfs = kern_mount(type);
> + gemfs = vfs_kern_mount(type, SB_KERNMOUNT, type->name, opts);
> if (IS_ERR(gemfs))
> return PTR_ERR(gemfs);
>
> i915->mm.gemfs = gemfs;
>
> + drm_info(&i915->drm, "Transparent Hugepage mode '%s'", opts);
> +
> return 0;
> }
>
> --
> 2.30.2
>
