linux-kernel - Re: [PATCH 09/13] drm/i915: don't use gtt

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Date:	Sun, 06 Nov 2011 21:16:00 +0000
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Daniel Vetter <daniel.vetter@...ll.ch>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>
Cc:	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH 09/13] drm/i915: don't use gtt_pwrite on LLC cached objects

On Sun,  6 Nov 2011 20:13:56 +0100, Daniel Vetter <daniel.vetter@...ll.ch> wrote:
> ~120 µs instead fo ~210 µs to write 1mb on my snb. I like this.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>
> ---
>  drivers/gpu/drm/i915/i915_gem.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 0048917..8fd175c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -842,6 +842,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
>  		ret = i915_gem_phys_pwrite(dev, obj, args, file);
>  		goto out;
>  	} else if (obj->gtt_space &&
> +		   obj->cache_level == I915_CACHE_NONE &&
>  		   obj->base.write_domain != I915_GEM_DOMAIN_CPU) {
>  		ret = i915_gem_object_pin(obj, 0, true);
>  		if (ret)

I still think you want to include a obj->map_and_fenceable test here.
When doing 2D benchmarks the stall incurred here to evict an old object
map the to-be-written object into the mappable GTT causes measureable
pain (obviously on non-LLC architectures).

The series looks good and I'll look at the impact upon 2D for pnv and
snb over the next couple of days. With and without the extra check ;-)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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