Re: [PATCH v2 3/6] drm/i915: Use WC copies on !llc platforms for the command parser

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH v2 3/6] drm/i915: Use WC copies on !llc platforms for the command parser
Date: Fri, 20 Nov 2015 17:05:05 +0200	[thread overview]
Message-ID: <20151120150505.GN4437@intel.com> (raw)
In-Reply-To: <1448016961-25331-4-git-send-email-chris@chris-wilson.co.uk>

On Fri, Nov 20, 2015 at 10:55:58AM +0000, Chris Wilson wrote:
> Since we blow the TLB caches by using kmap/kunmap, we may as well go the
> whole hog and see if declaring our destination page as WC is faster than
> keeping it as WB and using clflush. It should be!

Is this description for another patch? I can't see any WC stuff in
there.

> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_cmd_parser.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
> index c6f6d9f2b2ce..4a3e90b042c5 100644
> --- a/drivers/gpu/drm/i915/i915_cmd_parser.c
> +++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
> @@ -992,9 +992,10 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>  	const struct drm_i915_cmd_descriptor *desc = &default_desc;
>  	u32 last_cmd_header = 0;
>  	unsigned dst_iter, src_iter;
> -	int needs_clflush = 0;
>  	struct get_page rewind;
>  	void *src, *dst, *tmp;
> +	int src_needs_clflush = 0;
> +	bool dst_needs_clflush;
>  	u32 partial, length = 1;
>  	unsigned in, out;
>  	bool oacontrol_set = false; /* OACONTROL tracking. See check_cmd() */
> @@ -1007,13 +1008,19 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>  	if (WARN_ON(shadow_batch_obj->pages_pin_count == 0))
>  		return -ENODEV;
>  
> -	ret = i915_gem_obj_prepare_shmem_read(batch_obj, &needs_clflush);
> +	ret = i915_gem_obj_prepare_shmem_read(batch_obj, &src_needs_clflush);
>  	if (ret) {
>  		DRM_DEBUG_DRIVER("CMD: failed to prepare shadow batch\n");
>  		return ret;
>  	}
>  
> -	ret = i915_gem_object_set_to_cpu_domain(shadow_batch_obj, true);
> +	dst_needs_clflush =
> +		shadow_batch_obj->base.write_domain != I915_GEM_DOMAIN_CPU &&
> +		!INTEL_INFO(shadow_batch_obj->base.dev)->has_llc;
> +	if (dst_needs_clflush)
> +		ret = i915_gem_object_set_to_gtt_domain(shadow_batch_obj, true);
> +	else
> +		ret = i915_gem_object_set_to_cpu_domain(shadow_batch_obj, true);
>  	if (ret) {
>  		DRM_DEBUG_DRIVER("CMD: Failed to set shadow batch to CPU\n");
>  		goto unpin;
> @@ -1048,7 +1055,7 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>  			this = PAGE_SIZE - in;
>  
>  		src = kmap_atomic(i915_gem_object_get_page(batch_obj, src_iter));
> -		if (needs_clflush)
> +		if (src_needs_clflush)
>  			drm_clflush_virt_range(src + in, this);
>  
>  		if (this == PAGE_SIZE && partial == 0)
> @@ -1151,6 +1158,8 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>  				int len;
>  
>  				if (out == PAGE_SIZE) {
> +					if (dst_needs_clflush)
> +						drm_clflush_virt_range(dst, PAGE_SIZE);
>  					kunmap_atomic(dst);
>  					dst = kmap_atomic(i915_gem_object_get_page(shadow_batch_obj, ++dst_iter));
>  					out = 0;
> @@ -1179,6 +1188,8 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>  		kunmap_atomic(src);
>  		in = 0;
>  	}
> +	if (dst_needs_clflush)
> +		drm_clflush_virt_range(dst, out);
>  unmap:
>  	kunmap_atomic(src);
>  	kunmap_atomic(dst);
> -- 
> 2.6.2
> 
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC
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