Re: [PATCH 2/2] drm/i915: Use Transparent Hugepages when IOMMU is enabled

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx <Intel-gfx@lists.freedesktop.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Tvrtko Ursulin <tvrtko.ursulin@intel.com>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Matthew Auld <matthew.auld@intel.com>,
	Eero Tamminen <eero.t.tamminen@intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>
Subject: Re: [PATCH 2/2] drm/i915: Use Transparent Hugepages when IOMMU is enabled
Date: Tue, 7 Sep 2021 10:34:17 +0100	[thread overview]
Message-ID: <c58dd95e-3db0-9095-8f4e-bf3b9b6fda9c@linux.intel.com> (raw)
In-Reply-To: <YTcmCSr5HJZDeRNH@phenom.ffwll.local>

On 07/09/2021 09:42, Daniel Vetter wrote:
> On Fri, Sep 03, 2021 at 01:47:52PM +0100, Tvrtko Ursulin wrote:
>>
>> On 29/07/2021 15:06, Daniel Vetter wrote:
>>> On Thu, Jul 29, 2021 at 3:34 PM Tvrtko Ursulin
>>> <tvrtko.ursulin@linux.intel.com> wrote:
>>>>
>>>> From: Tvrtko Ursulin <tvrtko.ursulin@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).
>>>>
>>>> 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)
>>>>
>>>> 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@chris-wilson.co.uk>
>>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>>> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
>>>> Cc: Matthew Auld <matthew.auld@intel.com>
>>>> Cc: Eero Tamminen <eero.t.tamminen@intel.com>
>>>> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>>>> Cc: Daniel Vetter <daniel@ffwll.ch>
>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com> # v1
>>>
>>> On both patches: Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>>
>> Eero's testing results at
>> https://gitlab.freedesktop.org/drm/intel/-/issues/430 are looking good -
>> seem to show this to be a net win for at least Gen9 and Gen12 platforms.
>>
>> Is the ack enough to merge in this case or I should look for an r-b as well?
> 
> Since your back to defacto v1 with the 2nd patch I think you have full r-b
> already. So more than enough I think.

Just in case you missed it, v1 had Kconfig. But it's the same spirit so 
probably indeed fine as you say.

> Please do record the relative perf numbers from Eero in that issue in the
> commit message so that we have that on the git log record too. It's easier
> to find there than following the link and finding the right comment in the
> issue.

Will do.

Regards,

Tvrtko