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drm/i915: implement inline clflush for pwrite 

In micro-benchmarking of the usual pwrite use-pattern of alternating
pwrites with gtt domain reads from the gpu, this yields around 30%
improvement of pwrite throughput across all buffers size. The trick is
that we can avoid clflush cachelines that we will overwrite completely
anyway.

Furthermore for partial pwrites it gives a proportional speedup on top
of the 30% percent because we only clflush back the part of the buffer
we're actually writing.

v2: Simplify the clflush-before-write logic, as suggested by Chris
Wilson.

v3: Finishing touches suggested by Chris Wilson:
- add comment to needs_clflush_before and only set this if the bo is
  uncached.
- s/needs_clflush/needs_clflush_after/ in the write paths to clearly
  differentiate it from needs_clflush_before.

Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Daniel Vetter 2012-03-25 19:47:37 +02:00
parent 96d79b5270
commit 586428852a
1 changed files with 42 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

46
drivers/gpu/drm/i915/i915_gem.c
View File

@ -570,23 +570,39 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
int shmem_page_offset, page_length, ret = 0;
int obj_do_bit17_swizzling, page_do_bit17_swizzling;
int hit_slowpath = 0;
int needs_clflush_after = 0;
int needs_clflush_before = 0;
int release_page;
ret = i915_gem_object_set_to_cpu_domain(obj, 1);
if (ret)
return ret;
user_data = (char __user *) (uintptr_t) args->data_ptr;
remain = args->size;
obj_do_bit17_swizzling = i915_gem_object_needs_bit17_swizzle(obj);
if (obj->base.write_domain != I915_GEM_DOMAIN_CPU) {
/* If we're not in the cpu write domain, set ourself into the gtt
* write domain and manually flush cachelines (if required). This
* optimizes for the case when the gpu will use the data
* right away and we therefore have to clflush anyway. */
if (obj->cache_level == I915_CACHE_NONE)
needs_clflush_after = 1;
ret = i915_gem_object_set_to_gtt_domain(obj, true);
if (ret)
return ret;
}
/* Same trick applies for invalidate partially written cachelines before
* writing. */
if (!(obj->base.read_domains & I915_GEM_DOMAIN_CPU)
&& obj->cache_level == I915_CACHE_NONE)
needs_clflush_before = 1;
offset = args->offset;
obj->dirty = 1;
while (remain > 0) {
struct page *page;
char *vaddr;
int partial_cacheline_write;
/* Operation in this page
*
@ -599,6 +615,13 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
if ((shmem_page_offset + page_length) > PAGE_SIZE)
page_length = PAGE_SIZE - shmem_page_offset;
/* If we don't overwrite a cacheline completely we need to be
* careful to have up-to-date data by first clflushing. Don't
* overcomplicate things and flush the entire patch. */
partial_cacheline_write = needs_clflush_before &&
((shmem_page_offset | page_length)
& (boot_cpu_data.x86_clflush_size - 1));
if (obj->pages) {
page = obj->pages[offset >> PAGE_SHIFT];
release_page = 0;
@ -616,9 +639,15 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
if (!page_do_bit17_swizzling) {
vaddr = kmap_atomic(page);
if (partial_cacheline_write)
drm_clflush_virt_range(vaddr + shmem_page_offset,
page_length);
ret = __copy_from_user_inatomic(vaddr + shmem_page_offset,
user_data,
page_length);
if (needs_clflush_after)
drm_clflush_virt_range(vaddr + shmem_page_offset,
page_length);
kunmap_atomic(vaddr);
if (ret == 0)
@ -630,6 +659,9 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
mutex_unlock(&dev->struct_mutex);
vaddr = kmap(page);
if (partial_cacheline_write)
drm_clflush_virt_range(vaddr + shmem_page_offset,
page_length);
if (page_do_bit17_swizzling)
ret = __copy_from_user_swizzled(vaddr, shmem_page_offset,
user_data,
@ -638,6 +670,9 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
ret = __copy_from_user(vaddr + shmem_page_offset,
user_data,
page_length);
if (needs_clflush_after)
drm_clflush_virt_range(vaddr + shmem_page_offset,
page_length);
kunmap(page);
mutex_lock(&dev->struct_mutex);
@ -671,6 +706,9 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
}
}
if (needs_clflush_after)
intel_gtt_chipset_flush();
return ret;
}