From: Dave Gordon <david.s.gordon@xxxxxxxxx>
Avoiding the out-of-line call to sg_next() reduces the kernel execution
overhead by 10% in some workloads (for example the Unreal Engine 4 demo
Atlantis on 2GiB GTTs) which are dominated by the cost of inserting PTEs
due to texture thrashing. We can demonstrate this in a microbenchmark
that forces us to rebind the object on every execbuf, where we can
measure a 25% improvement, in the time required to execute an execbuf
requiring a texture to be rebound, for inlining the sg_next() for large
texture sizes.
Benchmark: igt/benchmarks/gem_exec_fault
Benchmark: igt/benchmarks/gem_exec_trace/Atlantis
Signed-off-by: Dave Gordon <david.s.gordon@xxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_drv.h | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 63ff5fa2b2bd..e2abd9eb352b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2278,6 +2278,25 @@ static __always_inline struct sgt_iter {
}
/**
+ * __sg_next - return the next scatterlist entry in a list
+ * @sg: The current sg entry
+ *
+ * Description:
+ * If the entry is the last, return NULL; otherwise, step to the next
+ * element in the array (@sg@+1). If that's a chain pointer, follow it;
+ * otherwise just return the pointer to the current element.
+ **/
+static inline struct scatterlist *__sg_next(struct scatterlist *sg)
+{
+#ifdef CONFIG_DEBUG_SG
+ BUG_ON(sg->sg_magic != SG_MAGIC);
+#endif
+ return sg_is_last(sg) ? NULL :
+ likely(!sg_is_chain(++sg)) ? sg :
+ sg_chain_ptr(sg);
+}
+
+/**
* for_each_sgt_dma - iterate over the DMA addresses of the given sg_table
* @__dmap: DMA address (output)
* @__iter: 'struct sgt_iter' (iterator state, internal)
@@ -2287,7 +2306,7 @@ static __always_inline struct sgt_iter {
for ((__iter) = __sgt_iter((__sgt)->sgl, true); \
((__dmap) = (__iter).dma + (__iter).curr); \
(((__iter).curr += PAGE_SIZE) < (__iter).max) || \
- ((__iter) = __sgt_iter(sg_next((__iter).sgp), true), 0))
+ ((__iter) = __sgt_iter(__sg_next((__iter).sgp), true), 0))
/**
* for_each_sgt_page - iterate over the pages of the given sg_table
@@ -2300,7 +2319,7 @@ static __always_inline struct sgt_iter {
((__pp) = (__iter).pfn == 0 ? NULL : \
pfn_to_page((__iter).pfn + ((__iter).curr >> PAGE_SHIFT))); \
(((__iter).curr += PAGE_SIZE) < (__iter).max) || \
- ((__iter) = __sgt_iter(sg_next((__iter).sgp), false), 0))
+ ((__iter) = __sgt_iter(__sg_next((__iter).sgp), false), 0))
/**
* Request queue structure.
--
2.8.1
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