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Subject[PATCH v4 8/9] gpu/drm/i915: optimize out the case when a range is updated to read only
Date
From: Jérôme Glisse <jglisse@redhat.com>

When range of virtual address is updated read only and corresponding
user ptr object are already read only it is pointless to do anything.
Optimize this case out.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ross Zwisler <zwisler@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: kvm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-rdma@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
---
drivers/gpu/drm/i915/i915_gem_userptr.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 9558582c105e..23330ac3d7ea 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -59,6 +59,7 @@ struct i915_mmu_object {
struct interval_tree_node it;
struct list_head link;
struct work_struct work;
+ bool read_only;
bool attached;
};

@@ -119,6 +120,7 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
container_of(_mn, struct i915_mmu_notifier, mn);
struct i915_mmu_object *mo;
struct interval_tree_node *it;
+ bool update_to_read_only;
LIST_HEAD(cancelled);
unsigned long end;

@@ -128,6 +130,8 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
/* interval ranges are inclusive, but invalidate range is exclusive */
end = range->end - 1;

+ update_to_read_only = mmu_notifier_range_update_to_read_only(range);
+
spin_lock(&mn->lock);
it = interval_tree_iter_first(&mn->objects, range->start, end);
while (it) {
@@ -145,6 +149,17 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
* object if it is not in the process of being destroyed.
*/
mo = container_of(it, struct i915_mmu_object, it);
+
+ /*
+ * If it is already read only and we are updating to
+ * read only then we do not need to change anything.
+ * So save time and skip this one.
+ */
+ if (update_to_read_only && mo->read_only) {
+ it = interval_tree_iter_next(it, range->start, end);
+ continue;
+ }
+
if (kref_get_unless_zero(&mo->obj->base.refcount))
queue_work(mn->wq, &mo->work);

@@ -270,6 +285,7 @@ i915_gem_userptr_init__mmu_notifier(struct drm_i915_gem_object *obj,
mo->mn = mn;
mo->obj = obj;
mo->it.start = obj->userptr.ptr;
+ mo->read_only = i915_gem_object_is_readonly(obj);
mo->it.last = obj->userptr.ptr + obj->base.size - 1;
INIT_WORK(&mo->work, cancel_userptr);

--
2.17.2
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