[PATCH v3 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c

Zhao Liu
2023-12-03T13:18:49Z

kmap_local_page()[1], and this patch converts the calls from
kmap_atomic() to kmap_local_page().

The main difference between atomic and local mappings is that local
mappings doesn't disable page faults or preemption (the preemption is
disabled for !PREEMPT_RT case, otherwise it only disables migration).

With kmap_local_page(), we can avoid the often unwanted side effect of
unnecessary page faults and preemption disables.

In i915_gem_execbuffer.c, eb->reloc_cache.vaddr is mapped by
kmap_atomic() in eb_relocate_entry(), and is unmapped by
kunmap_atomic() in reloc_cache_reset().

And this mapping/unmapping occurs in two places: one is in
eb_relocate_vma(), and another is in eb_relocate_vma_slow().

The function eb_relocate_vma() or eb_relocate_vma_slow() doesn't
need to disable pagefaults and preemption during the above mapping/
unmapping.

So it can simply use kmap_local_page() / kunmap_local() that can
instead do the mapping / unmapping regardless of the context.

Convert the calls of kmap_atomic() / kunmap_atomic() to
kmap_local_page() / kunmap_local().

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
Suggested by credits:
Ira: Referred to his task document, review comments.
Fabio: Referred to his boiler plate commit message and his description
about why kmap_local_page() should be preferred.
---
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 683fd8d3151c..18b0f3117074 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1156,7 +1156,7 @@ static void reloc_cache_unmap(struct reloc_cache *cache)

vaddr = unmask_page(cache->vaddr);
if (cache->vaddr & KMAP)
- kunmap_atomic(vaddr);
+ kunmap_local(vaddr);
else
io_mapping_unmap_atomic((void __iomem *)vaddr);
}
@@ -1172,7 +1172,7 @@ static void reloc_cache_remap(struct reloc_cache *cache,
if (cache->vaddr & KMAP) {
struct page *page = i915_gem_object_get_page(obj, cache->page);

- vaddr = kmap_atomic(page);
+ vaddr = kmap_local_page(page);
cache->vaddr = unmask_flags(cache->vaddr) |
(unsigned long)vaddr;
} else {
@@ -1202,7 +1202,7 @@ static void reloc_cache_reset(struct reloc_cache *cache, struct i915_execbuffer
if (cache->vaddr & CLFLUSH_AFTER)
mb();

- kunmap_atomic(vaddr);
+ kunmap_local(vaddr);
i915_gem_object_finish_access(obj);
} else {
struct i915_ggtt *ggtt = cache_to_ggtt(cache);
@@ -1234,7 +1234,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj,
struct page *page;

if (cache->vaddr) {
- kunmap_atomic(unmask_page(cache->vaddr));
+ kunmap_local(unmask_page(cache->vaddr));
} else {
unsigned int flushes;
int err;
@@ -1256,7 +1256,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj,
if (!obj->mm.dirty)
set_page_dirty(page);

- vaddr = kmap_atomic(page);
+ vaddr = kmap_local_page(page);
cache->vaddr = unmask_flags(cache->vaddr) | (unsigned long)vaddr;
cache->page = pageno;

--
2.34.1