Attachment 48075 Details for Bug 38115 – Disable page faults for the fast paths

[patch] Disable page faults for the fast paths

0001-drm-i915-Disable-page-faults-around-the-fast-pwrite-.patch (text/plain), 3.40 KB, created by Chris Wilson on 2011-06-17 00:01:06 UTC

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Creator: Chris Wilson

Created: 2011-06-17 00:01:06 UTC

Size: 3.40 KB

patch

obsolete

>From e75582c40a71a90a2e8ac84178a5c574568120ac Mon Sep 17 00:00:00 2001
>From: Chris Wilson <chris@chris-wilson.co.uk>
>Date: Fri, 10 Jun 2011 21:04:13 +0100
>Subject: [PATCH] drm/i915: Disable page-faults around the fast pwrite/pread
> paths
>
>These paths hold onto the struct mutex whilst accessing pages. In
>order, to prevent a recursive dead-lock should we fault-in a GTT mapped
>page we need to return -EFAULT and fallback to the slow path.
>
>Lockdep has complained before about the potential dead-lock, but rvis is
>the first application found to sufficiently abuse the API to trigger it.
>
>Performance regression testing on a 1GiB PineView system using x11perf,
>cairo-perf-trace, glxgears and a few game benchmarks suggested no large
>regressions with just a 2% slowdown for firefox. The caveat is that this
>was an otherwise idle system.
>
>Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38115
>Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>---
> drivers/gpu/drm/i915/i915_gem.c |   32 ++++++++++++++++++++++++--------
> 1 files changed, 24 insertions(+), 8 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>index 890af70..896b26e 100644
>--- a/drivers/gpu/drm/i915/i915_gem.c
>+++ b/drivers/gpu/drm/i915/i915_gem.c
>@@ -362,9 +362,13 @@ i915_gem_shmem_pread_fast(struct drm_device *dev,
> 			page_length = PAGE_SIZE - page_offset;
> 
> 		page = read_cache_page_gfp(mapping, offset >> PAGE_SHIFT,
>-					   GFP_HIGHUSER | __GFP_RECLAIMABLE);
>-		if (IS_ERR(page))
>-			return PTR_ERR(page);
>+					   GFP_ATOMIC | GFP_HIGHUSER | __GFP_RECLAIMABLE);
>+		if (IS_ERR(page)) {
>+			/* Discard the original failure code so that we try
>+			 * again in the non-atomic slow path.
>+			 */
>+			return -EFAULT;
>+		}
> 
> 		vaddr = kmap_atomic(page);
> 		ret = __copy_to_user_inatomic(user_data,
>@@ -556,8 +560,11 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
> 		goto out;
> 
> 	ret = -EFAULT;
>-	if (!i915_gem_object_needs_bit17_swizzle(obj))
>+	if (!i915_gem_object_needs_bit17_swizzle(obj)) {
>+		pagefault_disable();
> 		ret = i915_gem_shmem_pread_fast(dev, obj, args, file);
>+		pagefault_enable();
>+	}
> 	if (ret == -EFAULT)
> 		ret = i915_gem_shmem_pread_slow(dev, obj, args, file);
> 
>@@ -798,9 +805,13 @@ i915_gem_shmem_pwrite_fast(struct drm_device *dev,
> 			page_length = PAGE_SIZE - page_offset;
> 
> 		page = read_cache_page_gfp(mapping, offset >> PAGE_SHIFT,
>-					   GFP_HIGHUSER | __GFP_RECLAIMABLE);
>-		if (IS_ERR(page))
>-			return PTR_ERR(page);
>+					   GFP_ATOMIC | GFP_HIGHUSER | __GFP_RECLAIMABLE);
>+		if (IS_ERR(page)) {
>+			/* Discard the original failure code so that we try
>+			 * again in the non-atomic slow path.
>+			 */
>+			return -EFAULT;
>+		}
> 
> 		vaddr = kmap_atomic(page, KM_USER0);
> 		ret = __copy_from_user_inatomic(vaddr + page_offset,
>@@ -1013,7 +1024,9 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
> 		if (ret)
> 			goto out_unpin;
> 
>+		pagefault_disable();
> 		ret = i915_gem_gtt_pwrite_fast(dev, obj, args, file);
>+		pagefault_enable();
> 		if (ret == -EFAULT)
> 			ret = i915_gem_gtt_pwrite_slow(dev, obj, args, file);
> 
>@@ -1025,8 +1038,11 @@ out_unpin:
> 			goto out;
> 
> 		ret = -EFAULT;
>-		if (!i915_gem_object_needs_bit17_swizzle(obj))
>+		if (!i915_gem_object_needs_bit17_swizzle(obj)) {
>+			pagefault_disable();
> 			ret = i915_gem_shmem_pwrite_fast(dev, obj, args, file);
>+			pagefault_enable();
>+		}
> 		if (ret == -EFAULT)
> 			ret = i915_gem_shmem_pwrite_slow(dev, obj, args, file);
> 	}
>-- 
>1.7.5.4
>

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Attachments on bug 38115: 47773 | 47828 | 48075 | 48197 | 48198

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