Re: [Intel-gfx] [PATCH v2 3/3] drm/i915: Limit the scattergather coalescing to 32bits

[Chris Wilson]

On Tue, Oct 18, 2016 at 10:33:11AM +0100, Tvrtko Ursulin wrote:
> 
> On 17/10/2016 09:00, Chris Wilson wrote:
> >The scattergather list uses a 32bit size counter, we should avoid
> >exceeding it.
> >
> >v2: Also we should use unsigned int to match sg->length.
> >
> >Fixes: 871dfbd67d4e ("drm/i915: Allow compaction upto SWIOTLB max segment 
> >size")
> >Signed-off-by: Chris Wilson 
> >Reviewed-by: Tvrtko Ursulin  # v1
> >---
> >  drivers/gpu/drm/i915/i915_gem.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem.c 
> >b/drivers/gpu/drm/i915/i915_gem.c
> >index 181bda2db587..a74ec10a5370 100644
> >--- a/drivers/gpu/drm/i915/i915_gem.c
> >+++ b/drivers/gpu/drm/i915/i915_gem.c
> >@@ -2205,7 +2205,7 @@ i915_gem_object_put_pages(struct drm_i915_gem_object 
> >*obj)
> > return 0;
> >  }
> >-static unsigned long swiotlb_max_size(void)
> >+static unsigned int swiotlb_max_size(void)
> >  {
> >  #if IS_ENABLED(CONFIG_SWIOTLB)
> > return rounddown(swiotlb_nr_tbl() << IO_TLB_SHIFT, PAGE_SIZE);
> >@@ -2225,7 +2225,7 @@ i915_gem_object_get_pages_gtt(struct 
> >drm_i915_gem_object *obj)
> > struct sgt_iter sgt_iter;
> > struct page *page;
> > unsigned long last_pfn = 0; /* suppress gcc warning */
> >-unsigned long max_segment;
> >+unsigned int max_segment;
> > int ret;
> > gfp_t gfp;
> >@@ -2238,7 +2238,7 @@ i915_gem_object_get_pages_gtt(struct 
> >drm_i915_gem_object *obj)
> > max_segment = swiotlb_max_size();
> > if (!max_segment)
> >-max_segment = obj->base.size;
> >+max_segment = rounddown(UINT_MAX, PAGE_SIZE);
> 
> rounddown looks like an overkill vs just UINT_MAX, no?

I think there is a subtle difference becuase we are couting in pages and
compare sg->length >= max_segment. If we left it at UINT_MAX, sg->length
would wrap to zero rather than start a new sg.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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Re: [Intel-gfx] [PATCH v2 3/3] drm/i915: Limit the scattergather coalescing to 32bits

[Tvrtko Ursulin]

On 17/10/2016 09:00, Chris Wilson wrote:

The scattergather list uses a 32bit size counter, we should avoid
exceeding it.

v2: Also we should use unsigned int to match sg->length.

Fixes: 871dfbd67d4e ("drm/i915: Allow compaction upto SWIOTLB max segment size")
Signed-off-by: Chris Wilson 
Reviewed-by: Tvrtko Ursulin  # v1
---
  drivers/gpu/drm/i915/i915_gem.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 181bda2db587..a74ec10a5370 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2205,7 +2205,7 @@ i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
return 0;
  }
  
-static unsigned long swiotlb_max_size(void)

+static unsigned int swiotlb_max_size(void)
  {
  #if IS_ENABLED(CONFIG_SWIOTLB)
return rounddown(swiotlb_nr_tbl() << IO_TLB_SHIFT, PAGE_SIZE);
@@ -2225,7 +2225,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object 
*obj)
struct sgt_iter sgt_iter;
struct page *page;
unsigned long last_pfn = 0; /* suppress gcc warning */
-   unsigned long max_segment;
+   unsigned int max_segment;
int ret;
gfp_t gfp;
  
@@ -2238,7 +2238,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
  
  	max_segment = swiotlb_max_size();

if (!max_segment)
-   max_segment = obj->base.size;
+   max_segment = rounddown(UINT_MAX, PAGE_SIZE);


rounddown looks like an overkill vs just UINT_MAX, no?

  
  	st = kmalloc(sizeof(*st), GFP_KERNEL);

if (st == NULL)


Anyway,

Reviewed-by: Tvrtko Ursulin 

Regards,

Tvrtko

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[Intel-gfx] [PATCH v2 3/3] drm/i915: Limit the scattergather coalescing to 32bits

[Chris Wilson]

The scattergather list uses a 32bit size counter, we should avoid
exceeding it.

v2: Also we should use unsigned int to match sg->length.

Fixes: 871dfbd67d4e ("drm/i915: Allow compaction upto SWIOTLB max segment size")
Signed-off-by: Chris Wilson 
Reviewed-by: Tvrtko Ursulin  # v1
---
 drivers/gpu/drm/i915/i915_gem.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 181bda2db587..a74ec10a5370 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2205,7 +2205,7 @@ i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
return 0;
 }
 
-static unsigned long swiotlb_max_size(void)
+static unsigned int swiotlb_max_size(void)
 {
 #if IS_ENABLED(CONFIG_SWIOTLB)
return rounddown(swiotlb_nr_tbl() << IO_TLB_SHIFT, PAGE_SIZE);
@@ -2225,7 +2225,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object 
*obj)
struct sgt_iter sgt_iter;
struct page *page;
unsigned long last_pfn = 0; /* suppress gcc warning */
-   unsigned long max_segment;
+   unsigned int max_segment;
int ret;
gfp_t gfp;
 
@@ -2238,7 +2238,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object 
*obj)
 
max_segment = swiotlb_max_size();
if (!max_segment)
-   max_segment = obj->base.size;
+   max_segment = rounddown(UINT_MAX, PAGE_SIZE);
 
st = kmalloc(sizeof(*st), GFP_KERNEL);
if (st == NULL)
-- 
2.9.3

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