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drm/i915: Inline sg_next() for the optimised SGL iterator 

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@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1463741647-15666-5-git-send-email-chris@chris-wilson.co.uk
This commit is contained in:
Dave Gordon 2016-05-20 11:54:07 +01:00 committed by Chris Wilson
parent 85d1225ec0
commit 63d1532616
1 changed files with 21 additions and 2 deletions
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23
drivers/gpu/drm/i915/i915_drv.h
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@ -2277,6 +2277,25 @@ static __always_inline struct sgt_iter {
return s;
}
/**
* __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)
@ -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.