linux-kernel - [PATCH v4 8/9] gpu/drm/i915: optimize out the case when a range is updated to read only

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Date:   Wed, 23 Jan 2019 17:23:14 -0500
From:   jglisse@...hat.com
To:     linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Christian König <christian.koenig@....com>,
        Jan Kara <jack@...e.cz>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>, kvm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v4 8/9] gpu/drm/i915: optimize out the case when a range is updated to read only

From: Jérôme Glisse <jglisse@...hat.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@...hat.com>
Cc: Christian König <christian.koenig@....com>
Cc: Jan Kara <jack@...e.cz>
Cc: Felix Kuehling <Felix.Kuehling@....com>
Cc: Jason Gunthorpe <jgg@...lanox.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Matthew Wilcox <mawilcox@...rosoft.com>
Cc: Ross Zwisler <zwisler@...nel.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Ralph Campbell <rcampbell@...dia.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: kvm@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org
Cc: linux-rdma@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.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