Re: [PATCH 1/6] drm/i915: Eliminate vmap overhead for cmd parser

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On Thu, Oct 01, 2015 at 12:57:10PM +0100, Chris Wilson wrote:
> With a little complexity to handle cmds straddling page boundaries, we
> can completely avoiding having to vmap the batch and the shadow batch
> objects whilst running the command parser.
> 
> On ivb i7-3720MQ:
> 
> x11perf -dot before 54.3M, after 53.2M (max 203M)
> glxgears before 7110 fps, after 7300 fps (max 7860 fps)
> 
> Before:
> Time to blt 16384 bytes x      1:	 12.400µs, 1.2GiB/s
> Time to blt 16384 bytes x   4096:	  3.055µs, 5.0GiB/s
> 
> After:
> Time to blt 16384 bytes x      1:	  8.600µs, 1.8GiB/s
> Time to blt 16384 bytes x   4096:	  2.456µs, 6.2GiB/s

Numbers for the overall series (or individual patches would be even
better) are needed. I thought you have this neat script now to do that for
an entire series?
-Daniel

> 
> Removing the vmap is mostly a win, except we lose in a few cases where
> the batch size is greater than a page due to the extra complexity (loss
> of a simple cache efficient large copy, and boundary handling).
> 
> v2: Reorder so that we do check oacontrol remaining set at end-of-batch
> 
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/i915/i915_cmd_parser.c | 298 ++++++++++++++++-----------------
>  1 file changed, 146 insertions(+), 152 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
> index 237ff6884a22..91e4baa0f2b8 100644
> --- a/drivers/gpu/drm/i915/i915_cmd_parser.c
> +++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
> @@ -852,100 +852,6 @@ find_reg(const struct drm_i915_reg_descriptor *table,
>  	return NULL;
>  }
>  
> -static u32 *vmap_batch(struct drm_i915_gem_object *obj,
> -		       unsigned start, unsigned len)
> -{
> -	int i;
> -	void *addr = NULL;
> -	struct sg_page_iter sg_iter;
> -	int first_page = start >> PAGE_SHIFT;
> -	int last_page = (len + start + 4095) >> PAGE_SHIFT;
> -	int npages = last_page - first_page;
> -	struct page **pages;
> -
> -	pages = drm_malloc_ab(npages, sizeof(*pages));
> -	if (pages == NULL) {
> -		DRM_DEBUG_DRIVER("Failed to get space for pages\n");
> -		goto finish;
> -	}
> -
> -	i = 0;
> -	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, first_page) {
> -		pages[i++] = sg_page_iter_page(&sg_iter);
> -		if (i == npages)
> -			break;
> -	}
> -
> -	addr = vmap(pages, i, 0, PAGE_KERNEL);
> -	if (addr == NULL) {
> -		DRM_DEBUG_DRIVER("Failed to vmap pages\n");
> -		goto finish;
> -	}
> -
> -finish:
> -	if (pages)
> -		drm_free_large(pages);
> -	return (u32*)addr;
> -}
> -
> -/* Returns a vmap'd pointer to dest_obj, which the caller must unmap */
> -static u32 *copy_batch(struct drm_i915_gem_object *dest_obj,
> -		       struct drm_i915_gem_object *src_obj,
> -		       u32 batch_start_offset,
> -		       u32 batch_len)
> -{
> -	int needs_clflush = 0;
> -	void *src_base, *src;
> -	void *dst = NULL;
> -	int ret;
> -
> -	if (batch_len > dest_obj->base.size ||
> -	    batch_len + batch_start_offset > src_obj->base.size)
> -		return ERR_PTR(-E2BIG);
> -
> -	if (WARN_ON(dest_obj->pages_pin_count == 0))
> -		return ERR_PTR(-ENODEV);
> -
> -	ret = i915_gem_obj_prepare_shmem_read(src_obj, &needs_clflush);
> -	if (ret) {
> -		DRM_DEBUG_DRIVER("CMD: failed to prepare shadow batch\n");
> -		return ERR_PTR(ret);
> -	}
> -
> -	src_base = vmap_batch(src_obj, batch_start_offset, batch_len);
> -	if (!src_base) {
> -		DRM_DEBUG_DRIVER("CMD: Failed to vmap batch\n");
> -		ret = -ENOMEM;
> -		goto unpin_src;
> -	}
> -
> -	ret = i915_gem_object_set_to_cpu_domain(dest_obj, true);
> -	if (ret) {
> -		DRM_DEBUG_DRIVER("CMD: Failed to set shadow batch to CPU\n");
> -		goto unmap_src;
> -	}
> -
> -	dst = vmap_batch(dest_obj, 0, batch_len);
> -	if (!dst) {
> -		DRM_DEBUG_DRIVER("CMD: Failed to vmap shadow batch\n");
> -		ret = -ENOMEM;
> -		goto unmap_src;
> -	}
> -
> -	src = src_base + offset_in_page(batch_start_offset);
> -	if (needs_clflush)
> -		drm_clflush_virt_range(src, batch_len);
> -
> -	memcpy(dst, src, batch_len);
> -
> -unmap_src:
> -	vunmap(src_base);
> -unpin_src:
> -	i915_gem_object_unpin_pages(src_obj);
> -
> -	return ret ? ERR_PTR(ret) : dst;
> -}
> -
>  /**
>   * i915_needs_cmd_parser() - should a given ring use software command parsing?
>   * @ring: the ring in question
> @@ -1112,16 +1018,35 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>  		    u32 batch_len,
>  		    bool is_master)
>  {
> -	u32 *cmd, *batch_base, *batch_end;
> +	u32 tmp[128];
> +	const struct drm_i915_cmd_descriptor *desc;
> +	unsigned dst_iter, src_iter;
> +	int needs_clflush = 0;
> +	struct get_page rewind;
> +	void *src, *dst;
> +	unsigned in, out;
> +	u32 *buf, partial = 0, length;
>  	struct drm_i915_cmd_descriptor default_desc = { 0 };
>  	bool oacontrol_set = false; /* OACONTROL tracking. See check_cmd() */
>  	int ret = 0;
>  
> -	batch_base = copy_batch(shadow_batch_obj, batch_obj,
> -				batch_start_offset, batch_len);
> -	if (IS_ERR(batch_base)) {
> -		DRM_DEBUG_DRIVER("CMD: Failed to copy batch\n");
> -		return PTR_ERR(batch_base);
> +	if (batch_len > shadow_batch_obj->base.size ||
> +	    batch_len + batch_start_offset > batch_obj->base.size)
> +		return -E2BIG;
> +
> +	if (WARN_ON(shadow_batch_obj->pages_pin_count == 0))
> +		return -ENODEV;
> +
> +	ret = i915_gem_obj_prepare_shmem_read(batch_obj, &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);
> +	if (ret) {
> +		DRM_DEBUG_DRIVER("CMD: Failed to set shadow batch to CPU\n");
> +		goto unpin;
>  	}
>  
>  	/*
> @@ -1129,69 +1054,138 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>  	 * large or larger and copy_batch() will write MI_NOPs to the extra
>  	 * space. Parsing should be faster in some cases this way.
>  	 */
> -	batch_end = batch_base + (batch_len / sizeof(*batch_end));
> +	ret = -EINVAL;
> +	rewind = batch_obj->get_page;
> +
> +	dst_iter = 0;
> +	dst = kmap_atomic(i915_gem_object_get_page(shadow_batch_obj, dst_iter));
> +
> +	in = offset_in_page(batch_start_offset);
> +	out = 0;
> +	for (src_iter = batch_start_offset >> PAGE_SHIFT;
> +	     src_iter < batch_obj->base.size >> PAGE_SHIFT;
> +	     src_iter++) {
> +		u32 this, i, j, k;
> +		u32 *cmd, *page_end, *batch_end;
> +
> +		this = batch_len;
> +		if (this > PAGE_SIZE - in)
> +			this = PAGE_SIZE - in;
> +
> +		src = kmap_atomic(i915_gem_object_get_page(batch_obj, src_iter));
> +		if (needs_clflush)
> +			drm_clflush_virt_range(src + in, this);
> +
> +		i = this;
> +		j = in;
> +		do {
> +			/* We keep dst around so that we do not blow
> +			 * the CPU caches immediately after the copy (due
> +			 * to the kunmap_atomic(dst) doing a TLB flush.
> +			 */
> +			if (out == PAGE_SIZE) {
> +				kunmap_atomic(dst);
> +				dst = kmap_atomic(i915_gem_object_get_page(shadow_batch_obj, ++dst_iter));
> +				out = 0;
> +			}
>  
> -	cmd = batch_base;
> -	while (cmd < batch_end) {
> -		const struct drm_i915_cmd_descriptor *desc;
> -		u32 length;
> +			k = i;
> +			if (k > PAGE_SIZE - out)
> +				k = PAGE_SIZE - out;
> +			if (k == PAGE_SIZE)
> +				copy_page(dst, src);
> +			else
> +				memcpy(dst + out, src + j, k);
> +
> +			out += k;
> +			j += k;
> +			i -= k;
> +		} while (i);
> +
> +		cmd = src + in;
> +		page_end = (void *)cmd + this;
> +		batch_end = (void *)cmd + batch_len;
> +
> +		if (partial) {
> +			memcpy(tmp + partial, cmd, (length - partial)*4);
> +			cmd -= partial;
> +			partial = 0;
> +			buf = tmp;
> +			goto check;
> +		}
>  
> -		if (*cmd == MI_BATCH_BUFFER_END)
> -			break;
> +		do {
> +			if (*cmd == MI_BATCH_BUFFER_END) {
> +				if (oacontrol_set) {
> +					DRM_DEBUG_DRIVER("CMD: batch set OACONTROL but did not clear it\n");
> +					ret = -EINVAL;
> +				} else
> +					ret = 0;
> +				goto unmap;
> +			}
>  
> -		desc = find_cmd(ring, *cmd, &default_desc);
> -		if (!desc) {
> -			DRM_DEBUG_DRIVER("CMD: Unrecognized command: 0x%08X\n",
> -					 *cmd);
> -			ret = -EINVAL;
> -			break;
> -		}
> +			desc = find_cmd(ring, *cmd, &default_desc);
> +			if (!desc) {
> +				DRM_DEBUG_DRIVER("CMD: Unrecognized command: 0x%08X\n",
> +						 *cmd);
> +				goto unmap;
> +			}
>  
> -		/*
> -		 * If the batch buffer contains a chained batch, return an
> -		 * error that tells the caller to abort and dispatch the
> -		 * workload as a non-secure batch.
> -		 */
> -		if (desc->cmd.value == MI_BATCH_BUFFER_START) {
> -			ret = -EACCES;
> -			break;
> -		}
> +			/*
> +			 * If the batch buffer contains a chained batch, return an
> +			 * error that tells the caller to abort and dispatch the
> +			 * workload as a non-secure batch.
> +			 */
> +			if (desc->cmd.value == MI_BATCH_BUFFER_START) {
> +				ret = -EACCES;
> +				goto unmap;
> +			}
>  
> -		if (desc->flags & CMD_DESC_FIXED)
> -			length = desc->length.fixed;
> -		else
> -			length = ((*cmd & desc->length.mask) + LENGTH_BIAS);
> -
> -		if ((batch_end - cmd) < length) {
> -			DRM_DEBUG_DRIVER("CMD: Command length exceeds batch length: 0x%08X length=%u batchlen=%td\n",
> -					 *cmd,
> -					 length,
> -					 batch_end - cmd);
> -			ret = -EINVAL;
> -			break;
> -		}
> +			if (desc->flags & CMD_DESC_FIXED)
> +				length = desc->length.fixed;
> +			else
> +				length = ((*cmd & desc->length.mask) + LENGTH_BIAS);
>  
> -		if (!check_cmd(ring, desc, cmd, length, is_master,
> -			       &oacontrol_set)) {
> -			ret = -EINVAL;
> -			break;
> -		}
> +			if (cmd + length > page_end) {
> +				if (length + cmd > batch_end) {
> +					DRM_DEBUG_DRIVER("CMD: Command length exceeds batch length: 0x%08X length=%u batchlen=%td\n",
> +							 *cmd, length, batch_end - cmd);
> +					goto unmap;
> +				}
>  
> -		cmd += length;
> -	}
> +				if (WARN_ON(length > sizeof(tmp)/4)) {
> +					ret = -ENODEV;
> +					goto unmap;
> +				}
>  
> -	if (oacontrol_set) {
> -		DRM_DEBUG_DRIVER("CMD: batch set OACONTROL but did not clear it\n");
> -		ret = -EINVAL;
> -	}
> +				partial = page_end - cmd;
> +				memcpy(tmp, cmd, partial*4);
> +				break;
> +			}
>  
> -	if (cmd >= batch_end) {
> -		DRM_DEBUG_DRIVER("CMD: Got to the end of the buffer w/o a BBE cmd!\n");
> -		ret = -EINVAL;
> -	}
> +			buf = cmd;
> +check:
> +			if (!check_cmd(ring, desc, buf, length, is_master,
> +				       &oacontrol_set))
> +				goto unmap;
>  
> -	vunmap(batch_base);
> +			cmd += length;
> +		} while (cmd < page_end);
> +
> +		batch_len -= this;
> +		if (batch_len == 0)
> +			break;
> +
> +		kunmap_atomic(src);
> +		in = 0;
> +	}
>  
> +unmap:
> +	kunmap_atomic(src);
> +	kunmap_atomic(dst);
> +	batch_obj->get_page = rewind;
> +unpin:
> +	i915_gem_object_unpin_pages(batch_obj);
>  	return ret;
>  }
>  
> -- 
> 2.6.0
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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