[PATCH 10/13] drm/i915: don't call shmem_read_mapping unnecessarily

Daniel Vetter
2011-11-06T19:13:57Z

This speeds up pwrite and pread from ~120 µs ro ~100 µs for
reading/writing 1mb on my snb (if the backing storage pages
are already pinned, of course).

v2: Chris Wilson pointed out a claring page reference bug - I've
unconditionally dropped the reference. With that fixed (and the
associated reduction of dirt in dmesg) it's now even a notch faster.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/i915/i915_gem.c | 42 +++++++++++++++++++++++++++++---------
1 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8fd175c..5b8a7c5 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -339,6 +339,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
int obj_do_bit17_swizzling, page_do_bit17_swizzling;
int hit_slowpath = 0;
int needs_clflush = 0;
+ int release_page;

user_data = (char __user *) (uintptr_t) args->data_ptr;
remain = args->size;
@@ -373,10 +374,16 @@ i915_gem_shmem_pread(struct drm_device *dev,
if ((shmem_page_offset + page_length) > PAGE_SIZE)
page_length = PAGE_SIZE - shmem_page_offset;

- page = shmem_read_mapping_page(mapping, offset >> PAGE_SHIFT);
- if (IS_ERR(page)) {
- ret = PTR_ERR(page);
- goto out;
+ if (obj->pages) {
+ page = obj->pages[offset >> PAGE_SHIFT];
+ release_page = 0;
+ } else {
+ page = shmem_read_mapping_page(mapping, offset >> PAGE_SHIFT);
+ if (IS_ERR(page)) {
+ ret = PTR_ERR(page);
+ goto out;
+ }
+ release_page = 1;
}

page_do_bit17_swizzling = (page_to_phys(page) & (1 << 17)) == 0;
@@ -395,6 +402,9 @@ i915_gem_shmem_pread(struct drm_device *dev,
}

hit_slowpath = 1;
+ if (!release_page)
+ page_cache_get(page);
+ release_page = 1;

mutex_unlock(&dev->struct_mutex);

@@ -416,7 +426,8 @@ i915_gem_shmem_pread(struct drm_device *dev,
mutex_lock(&dev->struct_mutex);
next_page:
mark_page_accessed(page);
- page_cache_release(page);
+ if (release_page)
+ page_cache_release(page);

if (ret) {
ret = -EFAULT;
@@ -697,6 +708,7 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
int shmem_page_offset, page_length, ret;
int obj_do_bit17_swizzling, page_do_bit17_swizzling;
int hit_slowpath = 0;
+ int release_page;

user_data = (char __user *) (uintptr_t) args->data_ptr;
remain = args->size;
@@ -721,10 +733,16 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
if ((shmem_page_offset + page_length) > PAGE_SIZE)
page_length = PAGE_SIZE - shmem_page_offset;

- page = shmem_read_mapping_page(mapping, offset >> PAGE_SHIFT);
- if (IS_ERR(page)) {
- ret = PTR_ERR(page);
- goto out;
+ if (obj->pages) {
+ page = obj->pages[offset >> PAGE_SHIFT];
+ release_page = 0;
+ } else {
+ page = shmem_read_mapping_page(mapping, offset >> PAGE_SHIFT);
+ if (IS_ERR(page)) {
+ ret = PTR_ERR(page);
+ goto out;
+ }
+ release_page = 1;
}

page_do_bit17_swizzling = (page_to_phys(page) & (1 << 17)) == 0;
@@ -741,6 +759,9 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
}

hit_slowpath = 1;
+ if (!release_page)
+ page_cache_get(page);
+ release_page = 1;

mutex_unlock(&dev->struct_mutex);

@@ -759,7 +780,8 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
next_page:
set_page_dirty(page);
mark_page_accessed(page);
- page_cache_release(page);
+ if (release_page)
+ page_cache_release(page);

if (ret) {
ret = -EFAULT;
--
1.7.6.4